From ntent at pctcnet.net Sun Mar 1 01:25:16 2009 From: ntent at pctcnet.net (ntent) Date: Sat, 28 Feb 2009 10:25:16 -0600 Subject: [ATM] Eyepiece question Message-ID: <49A9656C.2010403@pctcnet.net> I'd still like some opinions on this variable eyepiece I'm consideringn for my 6" scope. It is eBay item number 330310000830 No, I am not trying to direct anyone to the outfit selling this item, 'nor am I affiliated in any way with the seller. From rflrs at rcn.com Sun Mar 1 01:45:52 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Sat, 28 Feb 2009 11:45:52 -0500 Subject: [ATM] f/8 Cemented Petzval Message-ID: <49A96A40.8010803@rcn.com> Another cemented Petzval -- this one is all-Schott ECO. The crowns are well known. The flints may not be, but are relatively robust. OK, the CTE on the secondary is not quite matched, but at 4", it may not matter as much. Prescriptions for this 6" f/8 Petzval are relatively simple: http://users.rcn.com/rflrs/Ptz11-49x.atm ATMOS input file http://users.rcn.com/rflrs/Ptz11-49x.len OSLO input file http://users.rcn.com/rflrs/Ptz11-49x.txt TEXT prescription http://users.rcn.com/rflrs/Ptz11-49x.zmx ZEMAX input file This anastigmat's Visual Strehl is about 0.7 over the full 2 degree field. From rmay at nethere.com Sun Mar 1 08:20:07 2009 From: rmay at nethere.com (Bob May) Date: Sat, 28 Feb 2009 15:20:07 -0800 Subject: [ATM] Eyepiece question References: <49A9656C.2010403@pctcnet.net> Message-ID: <000801c999fb$19eeef20$8f78fea9@amd> I'd not consider buying any zoom type EP as they are all a severe comprimise as far as optics goes. Generally narrow filds of view and soft focus are the biggest problems right off the bat. If you want it as a toy, go ahead and buy it but it really isn't worth the prices for them. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From drgert1 at yahoo.com Sun Mar 1 08:29:35 2009 From: drgert1 at yahoo.com (Gert Gottschalk) Date: Sat, 28 Feb 2009 15:29:35 -0800 (PST) Subject: [ATM] Ronchi grating stripes In-Reply-To: <002a01c99937$f1fb5080$8f78fea9@amd> Message-ID: <441203.72474.qm@web45101.mail.sp1.yahoo.com> Hi All, I put a few photos of the Ronchi test issue online at: http://www.trivalleystargazers.org/gert/ronchitester/ronchi_tester.html There are a few ideas that I like you hear your comments on. Esp. with the goal to improve the Ronchi lines contrast in the last photo. 1. Investigate scattering in the (supposedly) clear film base 2. Create new Postscript file with modified Ronchi patterns as follows. 2.1. Wider black & smaller clear duty-cycle (all over) 2.2. Wider black & smaller clear at region only in front of light source. 2.3. Entirely new pattern with just 1 slit in front of light source (slit how wide with resp. to grating???) I would like to ask for your input on above plan and further suggestions. Thanks & Clear Skies, Gert From simo at simoivanov.com Sun Mar 1 09:10:02 2009 From: simo at simoivanov.com (simo ivanov) Date: Sun, 01 Mar 2009 09:10:02 +0900 Subject: [ATM] Eyepiece question In-Reply-To: <000801c999fb$19eeef20$8f78fea9@amd> References: <49A9656C.2010403@pctcnet.net> <000801c999fb$19eeef20$8f78fea9@amd> Message-ID: <49A9D25A.5080001@simoivanov.com> Not sure about your listing, as I don't know the company or the model, but I own a 8-24mm zoom eyepiece, and my experience with it is exactly the opposite of Bob's. The optics is excellent,the focus is very sharp (I can see no difference comparing it to other, non-zoom eyepieces from that focus range that I have tried), the large eye relief is great, and the FOV (about 42 to about 55 degrees or thereabouts, advertised as 42-60) is more than adequate. It is the most versatile eyepiece I have, and I, for one, don't leave home without it. It is definitely not a toy, but I agree that zoom is not the cheapest choice. Cheers, Bob May wrote: > I'd not consider buying any zoom type EP as they are all a severe > comprimise as far as optics goes. Generally narrow filds of view > and soft focus are the biggest problems right off the bat. If > you want it as a toy, go ahead and buy it but it really isn't > worth the prices for them. > Bob May > > rmay at nethere.com > http: slash /nav.to slash bobmay > http: slash /bobmay dot astronomy.net > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From burrjaw at earthlink.net Sun Mar 1 09:24:49 2009 From: burrjaw at earthlink.net (Jim Burrows) Date: Sat, 28 Feb 2009 16:24:49 -0800 Subject: [ATM] Ronchi grating stripes In-Reply-To: <441203.72474.qm@web45101.mail.sp1.yahoo.com> References: <002a01c99937$f1fb5080$8f78fea9@amd> <441203.72474.qm@web45101.mail.sp1.yahoo.com> Message-ID: At 2009-02-28 15:29 -0800, Gert Gottschalk wrote: >There are a few ideas that I like you hear your comments on. >Esp. with the goal to improve the Ronchi lines contrast in the last photo. I think I'll rev up my Diffract programming pencil to show what the various tests (including Ronchi) look like with a white source - might be pretty. I'll have to run 3 FFTs for the three primary colors. One could run the current Diffract version to simulate various choices for Ronchi placement, line spacing, etc. http://home.earthlink.net/~burrjaw/public/diffract.zip (2004-04-12, Win32, 375 k) More later, -- Jim Burrows -- http://home.earthlink.net/~burrjaw -- mailto:burrjaw at earthlink.net -- Seattle N47.4723 W122.3662 (WGS84) From drgert1 at yahoo.com Sun Mar 1 14:59:38 2009 From: drgert1 at yahoo.com (Gert Gottschalk) Date: Sat, 28 Feb 2009 21:59:38 -0800 (PST) Subject: [ATM] Ronchi grating stripes In-Reply-To: <002a01c99937$f1fb5080$8f78fea9@amd> Message-ID: <293907.93788.qm@web45110.mail.sp1.yahoo.com> Bob, I would like to mention that I saw your name in the credits lines of the Postscript file I use, so I would like to thank you for your involvement in the project. Thanks & Clear skies, Gert --- On Fri, 2/27/09, Bob May wrote: > From: Bob May > Subject: Re: [ATM] Ronchi grating stripes > To: atm at atmlist.net > Date: Friday, February 27, 2009, 4:02 PM > Things of importance that I know of are that the lines be > straight, solid and equally spaced across the film. ... From mbartels at bbastrodesigns.com Mon Mar 2 03:25:41 2009 From: mbartels at bbastrodesigns.com (Mel Bartels) Date: Sun, 1 Mar 2009 10:25:41 -0800 Subject: [ATM] mirror making - the biggest issue In-Reply-To: <2B7CBEEB62274B7485FA7BFF4624C5CB@niks03981037eb> References: <0DCD85C01CDB41ABBB69EEA2FBAC0F8F@niks03981037eb> <4232AFB980CD432897B027B36DB6C6FB@niks03981037eb> <2B7CBEEB62274B7485FA7BFF4624C5CB@niks03981037eb> Message-ID: <006701c99a9b$264feb70$72efc250$@com> Invariably the biggest issue in mirror making, particularly from those starting on the journey, those isolated from others, is the grinding strokes. 99% of the time it comes down to strokes innocently being done incorrectly. There's huge confusion about how long a 1/3 stroke. Then there's the larger issue that people do not accurately inspect their strokes. I see over and over again people insisting that they are doing 1/3 strokes, but in fact the strokes are something else. The strokes are done too heavily, or are off centered, or the tool and mirror are never rotated, or the strokes are prolonged too long while the grit is turned into dry mud. A significant problem is that many people's hands are simply too big for smaller mirrors. Small mirrors are not easy for experienced people necessarily. These are easily corrected in moments by in-person inspection with an experienced person observing. Perhaps people can go to the trouble of having someone video their work when things don't go well so that we can inspect remotely. Otherwise it is very difficult because you'll go off course worrying about grits and contamination and whatnot, never realizing that it's the strokes that are invariably the challenge. Mel Bartels From tcohen at blakeglobal.com Mon Mar 2 05:15:46 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Sun, 1 Mar 2009 12:15:46 -0800 Subject: [ATM] sub-diameter tool strokes Message-ID: In my very limited experience using a 50% sub-diameter tool with TOT, I found a key difficulty was identifying the "neutral" stroke that produces a spherical shape without zones. I have found that this occurs (for my particular tool) when the center of the tool is offset from the center of the mirror by an amount equal to one-half the mirror's diameter (i.e. centered at the mirror's 50% zone). I find that deviation from this offset produces zones, which are most noticeable at the center. If the tool is positioned closer to the center, for example centered at the mirror's 30% zone, then formation of a narrow central depression is generated. On the other hand, if the tool is positioned farther from the center, then a narrow central raised zone (a bump) is generated. It's my working assumption (although my experience is too limited at this point to say with any certainty) that the amount of correction applied, or change to the focal length, can be adjusted via the length of the stroke, with shorter strokes reducing the focal length and vice-a-versa. For example, a spherical deepening of the center as would be necessary during parabolization (or curing an oblate spheroid as in my case) would entail a short stroke, with the edge of the tool remaining well inside of the mirror's diameter. To date, I find this to be a much superior technique for evenly deepening the central region. The 'W' stroke, which is discussed in the literature for deepening the center, I find is difficult to control and therefore less desirable. The center over center long stroke (even if offset to the 20% zone) quickly produces a narrow central depression. These comments are based on my limited experience to date and are not construed as being authoritative in any way. From hermit at outofoptions.org Mon Mar 2 05:05:54 2009 From: hermit at outofoptions.org (hermit) Date: Sun, 01 Mar 2009 15:05:54 -0500 Subject: [ATM] mirror making - the biggest issue In-Reply-To: <006701c99a9b$264feb70$72efc250$@com> References: <0DCD85C01CDB41ABBB69EEA2FBAC0F8F@niks03981037eb> <4232AFB980CD432897B027B36DB6C6FB@niks03981037eb> <2B7CBEEB62274B7485FA7BFF4624C5CB@niks03981037eb> <006701c99a9b$264feb70$72efc250$@com> Message-ID: <49AAEAA2.6010907@outofoptions.org> After pretty much 'blowing it' on my first mirror, using 1/3 OVERHANG not 1/3 total movement (meaning 1/6 overhang), I cut a circle out of ply wood and made a bumper to keep me from going long. I have also used the sharpie to draw a circle on the back of the mirror for reference. Last mirror I just set the machine to 1/4 stroke. :D Ken Lowther Mel Bartels wrote: > Invariably the biggest issue in mirror making, particularly from those > starting on the journey, those isolated from others, is the grinding > strokes. > > > > 99% of the time it comes down to strokes innocently being done incorrectly. > There's huge confusion about how long a 1/3 stroke. Then there's the larger > issue that people do not accurately inspect their strokes. I see over and > over again people insisting that they are doing 1/3 strokes, but in fact the > strokes are something else. The strokes are done too heavily, or are off > centered, or the tool and mirror are never rotated, or the strokes are > prolonged too long while the grit is turned into dry mud. A significant > problem is that many people's hands are simply too big for smaller mirrors. > Small mirrors are not easy for experienced people necessarily. > > > > These are easily corrected in moments by in-person inspection with an > experienced person observing. Perhaps people can go to the trouble of > having someone video their work when things don't go well so that we can > inspect remotely. Otherwise it is very difficult because you'll go off > course worrying about grits and contamination and whatnot, never realizing > that it's the strokes that are invariably the challenge. > > > > Mel Bartels > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From wa4guu at verizon.net Mon Mar 2 07:39:27 2009 From: wa4guu at verizon.net (Jerry) Date: Sun, 01 Mar 2009 17:39:27 -0500 Subject: [ATM] mirror making - the biggest issue In-Reply-To: <006701c99a9b$264feb70$72efc250$@com> Message-ID: And occasionally it is not that strokes are innocently being done incorrectly, but an aversion to doing it as others advise and has been shown to be successful. Trying to find your own way can be a good trait, but usually it is a bad trait until you have done a proven way first. After having been successful doing something in a time proven manner, one might more easily see when some different home grown method is not working. There may be many ways that will work, but there are many more ways that will not. Jerry -----Original Message----- From: Mel Bartels Invariably the biggest issue in mirror making, particularly from those starting on the journey, those isolated from others, is the grinding strokes. 99% of the time it comes down to strokes innocently being done incorrectly. There's huge confusion about how long a 1/3 stroke. From foreilly at verizon.net Mon Mar 2 09:50:34 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Sun, 01 Mar 2009 19:50:34 -0500 Subject: [ATM] I am about to drill a hole in my aluminum tube Message-ID: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> I am about to drill an eyepiece hole in my aluminum tube, I would like a check on my arithmetic computations. The mirror is 12.25 inches in diameter. The focal length is 85 1/8 inches. The first surface of the mirror is 6 1/8 inches from the back end of the tube. The 90 inch long aluminum tube is somewhat oval, but not too bad. The diameter where I will put the eyepiece is 15 1/8 inches. The height of the two inch focuser is three inches. I come up with 81.75 inches from the back of the tube as the center point of the eyepiece hole. I would appreciate any thoughts on this matter. I made a bad mistake with a prior tube abd I would like to avoid any further probelms. Thank you. Francis J. O'Reilly From foreilly at verizon.net Mon Mar 2 09:53:43 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Sun, 01 Mar 2009 19:53:43 -0500 Subject: [ATM] Clarification Message-ID: <34FDFE2F8B514110A2C0EB17BAF7D02A@HELENYLCMWAV95> The height of the focuser is the racked in height, three inches. Francis J. O'Reilly From mbartels at bbastrodesigns.com Mon Mar 2 10:13:38 2009 From: mbartels at bbastrodesigns.com (Mel Bartels) Date: Sun, 1 Mar 2009 17:13:38 -0800 Subject: [ATM] Clarification In-Reply-To: <34FDFE2F8B514110A2C0EB17BAF7D02A@HELENYLCMWAV95> References: <34FDFE2F8B514110A2C0EB17BAF7D02A@HELENYLCMWAV95> Message-ID: <00d301c99ad4$263cc1b0$72b64510$@com> Just be careful of the true diagonal to racked in focuser height. Mounting focusers on tubes can result in a shorter length. I'd allow 3/4" focus adjustment on the inward side, so make the focal plane at least that much above the focuser's racked in height (with adapters). Finally, the optical alignment screws on the primary mirror mount - how much travel do they have? I'd put them in a middle position and then center the mirror mount accordingly. Mel Bartels >>> The height of the focuser is the racked in height, three inches. From rmay at nethere.com Mon Mar 2 11:50:00 2009 From: rmay at nethere.com (Bob May) Date: Sun, 1 Mar 2009 18:50:00 -0800 Subject: [ATM] I am about to drill a hole in my aluminum tube References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: <001901c99ae1$954de900$8f78fea9@amd> Do the math and see about where things are supposed to go. Then drill the holes from teh EP and end up with the holes for the primary. There ae a lot of holes at the top end of the scope and once you drill them, it is hard to move them somewhere else without major work. The primary being last means that you have an alsmost complete scope that you can actually look through and find out by experiment exactly where you want the primary to be. I prefer to put 3 blocks permanently attached to the tube that the mirror support will mount to. This will allow you to remove the mirror and cell and put it back in exactly the same way. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From shane at ct-astronomer.com Mon Mar 2 11:53:57 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Sun, 1 Mar 2009 21:53:57 -0500 Subject: [ATM] I am about to drill a hole in my aluminum tube In-Reply-To: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: Francis, Is it possible to take a conservative approach and put the focuser hole and secondary in first, and then determine exactly where the primary will mount? Sure you can calculate it really closely, but it's nice to have insurance. Best luck. Shane LaPierre On Mar 1, 2009, at 7:50 PM, Francis J. O'Reilly wrote: > I am about to drill an eyepiece hole in my aluminum tube, I would > like a check on my arithmetic computations. > > The mirror is 12.25 inches in diameter. The focal length is 85 1/8 > inches. The first surface of the mirror is 6 1/8 inches from the > back end of the tube. The 90 inch long aluminum tube is somewhat > oval, but not too bad. The diameter where I will put the eyepiece is > 15 1/8 inches. The height of the two inch focuser is three inches. > > I come up with 81.75 inches from the back of the tube as the center > point of the eyepiece hole. > > I would appreciate any thoughts on this matter. I made a bad mistake > with a prior tube abd I would like to avoid any further probelms. > > Thank you. > > Francis J. O'Reilly > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From foreilly at verizon.net Mon Mar 2 11:54:18 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Sun, 01 Mar 2009 21:54:18 -0500 Subject: [ATM] Clarification References: <783673.9761.qm@web110114.mail.gq1.yahoo.com> Message-ID: <1AFBC9C86CAA4DF8A09D65F060769605@HELENYLCMWAV95> John, I figure an inch Francis ----- Original Message ----- From: John Lynch To: Francis J. O'Reilly Sent: Sunday, March 01, 2009 8:07 PM Subject: Re: [ATM] Clarification Francis, Whats' the extra focuser travel, i.e., how much beyond the totally racked in height (3") are you going to put the focal plane? John Lynch --- On Sun, 3/1/09, Francis J. O'Reilly wrote: From: Francis J. O'Reilly Subject: [ATM] Clarification To: atm at atmlist.net Cc: "Dick Parker" Date: Sunday, March 1, 2009, 7:53 PM The height of the focuser is the racked in height, three inches. Francis J. O'Reilly _______________________________________________ ATM mailing list http://www.atmlist.net/ From foreilly at verizon.net Mon Mar 2 11:55:36 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Sun, 01 Mar 2009 21:55:36 -0500 Subject: [ATM] Clarification References: <34FDFE2F8B514110A2C0EB17BAF7D02A@HELENYLCMWAV95> <00d301c99ad4$263cc1b0$72b64510$@com> Message-ID: <4F8992962D0E4CEFA6AA32E9C1C2E216@HELENYLCMWAV95> Mel, Thank you for your counsel. All very relevant issues. Francis ----- Original Message ----- From: "Mel Bartels" To: Sent: Sunday, March 01, 2009 8:13 PM Subject: Re: [ATM] Clarification > Just be careful of the true diagonal to racked in focuser height. > Mounting > focusers on tubes can result in a shorter length. > > I'd allow 3/4" focus adjustment on the inward side, so make the focal > plane > at least that much above the focuser's racked in height (with adapters). > > Finally, the optical alignment screws on the primary mirror mount - how > much > travel do they have? I'd put them in a middle position and then center > the > mirror mount accordingly. > > Mel Bartels > >>>> > The height of the focuser is the racked in height, three inches. > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From foreilly at verizon.net Mon Mar 2 11:57:42 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Sun, 01 Mar 2009 21:57:42 -0500 Subject: [ATM] I am about to drill a hole in my aluminum tube References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: Shane and Bob, I've already mounted the primary. It is pretty heavy and I really don't have anyone at home to help me with it. I appreciate your suggestion, It's just a little late I acted prematurely. Francis ----- Original Message ----- From: "Shane LaPierre" To: "Francis J. O'Reilly" Cc: ; "Dick Parker" Sent: Sunday, March 01, 2009 9:53 PM Subject: Re: [ATM] I am about to drill a hole in my aluminum tube > Francis, > > Is it possible to take a conservative approach and put the focuser hole > and secondary in first, and then determine exactly where the primary will > mount? Sure you can calculate it really closely, but it's nice to have > insurance. Best luck. > > Shane LaPierre > > > On Mar 1, 2009, at 7:50 PM, Francis J. O'Reilly wrote: > >> I am about to drill an eyepiece hole in my aluminum tube, I would like a >> check on my arithmetic computations. >> >> The mirror is 12.25 inches in diameter. The focal length is 85 1/8 >> inches. The first surface of the mirror is 6 1/8 inches from the back >> end of the tube. The 90 inch long aluminum tube is somewhat oval, but >> not too bad. The diameter where I will put the eyepiece is 15 1/8 >> inches. The height of the two inch focuser is three inches. >> >> I come up with 81.75 inches from the back of the tube as the center >> point of the eyepiece hole. >> >> I would appreciate any thoughts on this matter. I made a bad mistake >> with a prior tube abd I would like to avoid any further probelms. >> >> Thank you. >> >> Francis J. O'Reilly >> >> _______________________________________________ >> ATM mailing list http://www.atmlist.net/ > > From hermit at outofoptions.org Mon Mar 2 14:10:06 2009 From: hermit at outofoptions.org (hermit) Date: Mon, 02 Mar 2009 00:10:06 -0500 Subject: [ATM] I am about to drill a hole in my aluminum tube In-Reply-To: References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: <49AB6A2E.1030803@outofoptions.org> If you error on the short side, you can always extend the eyepiece out some with an adapter or a ring to keep the eyepiece from seating all the way into the focuser. Ken Lowther Francis J. O'Reilly wrote: > Shane and Bob, > > I've already mounted the primary. It is pretty heavy and I really > don't have anyone at home to help me with it. I appreciate your > suggestion, It's just a little late I acted prematurely. > > Francis > ----- Original Message ----- From: "Shane LaPierre" > > To: "Francis J. O'Reilly" > Cc: ; "Dick Parker" > Sent: Sunday, March 01, 2009 9:53 PM > Subject: Re: [ATM] I am about to drill a hole in my aluminum tube > > >> Francis, >> >> Is it possible to take a conservative approach and put the focuser >> hole and secondary in first, and then determine exactly where the >> primary will mount? Sure you can calculate it really closely, but >> it's nice to have insurance. Best luck. >> >> Shane LaPierre >> >> >> On Mar 1, 2009, at 7:50 PM, Francis J. O'Reilly wrote: >> >>> I am about to drill an eyepiece hole in my aluminum tube, I would >>> like a check on my arithmetic computations. >>> >>> The mirror is 12.25 inches in diameter. The focal length is 85 1/8 >>> inches. The first surface of the mirror is 6 1/8 inches from the >>> back end of the tube. The 90 inch long aluminum tube is somewhat >>> oval, but not too bad. The diameter where I will put the eyepiece >>> is 15 1/8 inches. The height of the two inch focuser is three inches. >>> >>> I come up with 81.75 inches from the back of the tube as the center >>> point of the eyepiece hole. >>> >>> I would appreciate any thoughts on this matter. I made a bad mistake >>> with a prior tube abd I would like to avoid any further probelms. >>> >>> Thank you. >>> >>> Francis J. O'Reilly >>> >>> _______________________________________________ >>> ATM mailing list http://www.atmlist.net/ >> >> > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From jhm.vangastel at ziggo.nl Mon Mar 2 15:37:28 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Mon, 2 Mar 2009 07:37:28 +0100 Subject: [ATM] I am about to drill a hole in my aluminum tube References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: Francis, Assuming that (a) 3" is the height of the fully racked-in focuser and (b) the focal point is at the outer end of that 3" focuser (for the moment, we correct this at the end), the distance from the focal plane to the center of the tube (optical axis) is 12.25/2+(15.125-12.25)/2+3=10.56". The vertical distance from the mirror face to the center of the focuser hole is: 85.125-10.56= 74.56". The vertical distance from the back of the tube to the center of the focuser hole is: 74.56+6.125 = 80.69". The real focal point will not be at the end of the fully racked in 3 inch focuser, so to this 80.69", the focuser in travel that you want, has to be added. If the focuser in travel is 1.06 inch (say, 1 inch) your calculations are correct. This is how I always do the calculations. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Francis J. O'Reilly" To: Cc: "Dick Parker" Sent: Monday, March 02, 2009 1:50 Subject: [ATM] I am about to drill a hole in my aluminum tube >I am about to drill an eyepiece hole in my aluminum tube, I would like a >check on my arithmetic computations. > > The mirror is 12.25 inches in diameter. The focal length is 85 1/8 inches. > The first surface of the mirror is 6 1/8 inches from the back end of the > tube. The 90 inch long aluminum tube is somewhat oval, but not too bad. > The diameter where I will put the eyepiece is 15 1/8 inches. The height of > the two inch focuser is three inches. > > I come up with 81.75 inches from the back of the tube as the center point > of the eyepiece hole. > > I would appreciate any thoughts on this matter. I made a bad mistake with > a prior tube abd I would like to avoid any further probelms. > > Thank you. > > Francis J. O'Reilly > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From neil at astronomy.ndo.co.uk Mon Mar 2 19:51:32 2009 From: neil at astronomy.ndo.co.uk (Neil Booker) Date: Mon, 2 Mar 2009 10:51:32 -0000 Subject: [ATM] I am about to drill a hole in my aluminum tube References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: <015801c99b25$3a4a1a80$ab9afea9@laura> ----- Original Message ----- From: "Francis J. O'Reilly" To: Sent: Monday, March 02, 2009 12:50 AM Subject: [ATM] I am about to drill a hole in my aluminum tube > I would appreciate any thoughts on this matter. I made a bad mistake with a prior tube abd I would like to avoid any further probelms. As a newbe I made that mistake. My scope could focus on the trees at the end of the garden but no farther. Our AS president joked that it'd make a good microscope. Certainly learned to measure twice, cut once then. Neil P.S. Using Richard Berry's Build your own telescope (page 27), I make it 79 11/16. ( Hole position = F + E - T/2 - H - 1 so Hole position = 85 1/8 + 6 1/8 - (15 1/8)/2 - 3 -1 = 79 11/16 ). As a newbe I'm hardly your peer so feel free to ignore this. From foreilly at verizon.net Mon Mar 2 21:04:35 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Mon, 02 Mar 2009 07:04:35 -0500 Subject: [ATM] I am about to drill a hole in my aluminum tube References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: <14CF1762FB0C4995BC31A765782CE5D7@HELENYLCMWAV95> Thank you Jan, I was looking for someone to independently verify my computations. I am also appreciative of the advice given by others. Best, Francis ----- Original Message ----- From: "Jan van Gastel" To: "Francis J. O'Reilly" ; Cc: "Dick Parker" Sent: Monday, March 02, 2009 1:37 AM Subject: Re: [ATM] I am about to drill a hole in my aluminum tube > Francis, > > Assuming that (a) 3" is the height of the fully racked-in focuser and (b) > the focal point is at the outer end of that 3" focuser (for the moment, we > correct this at the end), the distance from the focal plane to the center > of the tube (optical axis) is 12.25/2+(15.125-12.25)/2+3=10.56". The > vertical distance from the mirror face to the center of the focuser hole > is: 85.125-10.56= 74.56". The vertical distance from the back of the tube > to the center of the focuser hole is: 74.56+6.125 = 80.69". The real focal > point will not be at the end of the fully racked in 3 inch focuser, so to > this 80.69", the focuser in travel that you want, has to be added. If the > focuser in travel is 1.06 inch (say, 1 inch) your calculations are > correct. This is how I always do the calculations. > > Jan > http://members.ziggo.nl/jhm.vangastel/Astronomy/ > > > > ----- Original Message ----- > From: "Francis J. O'Reilly" > To: > Cc: "Dick Parker" > Sent: Monday, March 02, 2009 1:50 > Subject: [ATM] I am about to drill a hole in my aluminum tube > > >>I am about to drill an eyepiece hole in my aluminum tube, I would like a >>check on my arithmetic computations. >> >> The mirror is 12.25 inches in diameter. The focal length is 85 1/8 >> inches. The first surface of the mirror is 6 1/8 inches from the back end >> of the tube. The 90 inch long aluminum tube is somewhat oval, but not too >> bad. The diameter where I will put the eyepiece is 15 1/8 inches. The >> height of the two inch focuser is three inches. >> >> I come up with 81.75 inches from the back of the tube as the center point >> of the eyepiece hole. >> >> I would appreciate any thoughts on this matter. I made a bad mistake with >> a prior tube abd I would like to avoid any further probelms. >> >> Thank you. >> >> Francis J. O'Reilly >> >> _______________________________________________ >> ATM mailing list http://www.atmlist.net/ > > From smessner at rconnect.com Tue Mar 3 00:02:59 2009 From: smessner at rconnect.com (Steve Messner) Date: Mon, 02 Mar 2009 09:02:59 -0600 Subject: [ATM] I am about to drill a hole in my aluminum tube In-Reply-To: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: Hi, Also, you don't need a 2' hole to see if it focuses where you want. If your hole saw has a 1/4 bit, drill that first and test during the day or Moon, that will buy you almost +/- 1" if your planning on drilling a 2" hole. Steve M. PS; Sorry you got this twice Francis At 06:50 PM 3/1/2009, Francis J. O'Reilly wrote: >I am about to drill an eyepiece hole in my aluminum tube, I would >like a check on my arithmetic computations. > >The mirror is 12.25 inches in diameter. The focal length is 85 1/8 >inches. The first surface of the mirror is 6 1/8 inches from the >back end of the tube. The 90 inch long aluminum tube is somewhat >oval, but not too bad. The diameter where I will put the eyepiece is >15 1/8 inches. The height of the two inch focuser is three inches. > >I come up with 81.75 inches from the back of the tube as the center >point of the eyepiece hole. > >I would appreciate any thoughts on this matter. I made a bad mistake >with a prior tube abd I would like to avoid any further probelms. > >Thank you. > >Francis J. O'Reilly Clear Skies, Steve Messner Harvest Moon Observatory Northfield, MN 18" Newt. pc164, Kiwi, WAT-902H2 ULTIMATE Upper Mid-West Occultation page- http://www.harvestmoonorchard.com/astro/occultations/index.html From paul.kulyk at gmail.com Tue Mar 3 00:36:08 2009 From: paul.kulyk at gmail.com (Paul Kulyk) Date: Mon, 02 Mar 2009 09:36:08 -0600 Subject: [ATM] 8 inch f/5 too fast? Message-ID: <49ABFCE8.5010901@gmail.com> My original intent was to grind my 8 inch glass down to an f/6. At the end of WaO 25 things are looking now to be more of an f/5 or less! I had noticed this overshoot while I was in the #220 stage and had tried to correct it by working TOT through #220 even going back to #120 and using the grit I had left. Now I'm out of #120 have very little #220 and have a surface finished to the end of the WaO 25 stage. Will a scope of these proportions still be practical or will it be too short? I am also concerned about parabolizing this. Thank you for your thoughts. -- Paul From hermit at outofoptions.org Tue Mar 3 00:46:59 2009 From: hermit at outofoptions.org (hermit) Date: Mon, 02 Mar 2009 10:46:59 -0500 Subject: [ATM] 8 inch f/5 too fast? In-Reply-To: <49ABFCE8.5010901@gmail.com> References: <49ABFCE8.5010901@gmail.com> Message-ID: <49ABFF73.3020905@outofoptions.org> f/5 is fine. I chose that because it was considered the 'limit' before having to worry much about coma. Also, guy worried about focuser placement. I guess this is always an 'alternative' if you miss the placement. Regrind. :D Ken Lowther Paul Kulyk wrote: > My original intent was to grind my 8 inch glass down to an f/6. > > At the end of WaO 25 things are looking now to be more of an f/5 or less! > > I had noticed this overshoot while I was in the #220 stage and had tried > to correct it by working TOT through #220 even going back to #120 and > using the grit I had left. > > Now I'm out of #120 have very little #220 and have a surface finished to > the end of the WaO 25 stage. > > Will a scope of these proportions still be practical or will it be too > short? I am also concerned about parabolizing this. > > Thank you for your thoughts. > > From mjc5 at psu.edu Tue Mar 3 01:03:23 2009 From: mjc5 at psu.edu (Michael Coslo) Date: Mon, 02 Mar 2009 11:03:23 -0500 Subject: [ATM] 8 inch f/5 too fast? In-Reply-To: <49ABFCE8.5010901@gmail.com> References: <49ABFCE8.5010901@gmail.com> Message-ID: On Mar 2, 2009, at 10:36 AM, Paul Kulyk wrote: > My original intent was to grind my 8 inch glass down to an f/6. > > At the end of WaO 25 things are looking now to be more of an f/5 or > less! > > I had noticed this overshoot while I was in the #220 stage and had > tried > to correct it by working TOT through #220 even going back to #120 and > using the grit I had left. > > Now I'm out of #120 have very little #220 and have a surface > finished to > the end of the WaO 25 stage. > > Will a scope of these proportions still be practical or will it be too > short? I am also concerned about parabolizing this. > > Thank you for your thoughts. My decision would be based on whether or not I had the other parts of the scope made yet. If they were assembled and waiting for the mirror, then I suppose I'd lengthen the mirror a little bit. If not, I'd be the proud owner of an 8 inch F 5 mirror. This stuff happens, and there is no shame. That is the great thing about making your own scope. You can eat your mistakes for breakfast. 8^) Your scope will be a little shorter, a little lighter, and your eyepieces will give a larger field for a given mm size. That's good. There will be a bit more coma - although if it is at f5, it shouldn't be objectionable. And for your next scope, the best advice on keeping to the desired fl is to get it as close as possible on the first, coarse steps. I've been fascinated on the little tweaks that can be made even in fine grinding, but trying to shallow out a mirror by a large amount is pretty tough. -73 de Mike N3LI - From atm_ken_hunter at yahoo.com Tue Mar 3 02:04:16 2009 From: atm_ken_hunter at yahoo.com (Ken Hunter) Date: Mon, 2 Mar 2009 09:04:16 -0800 (PST) Subject: [ATM] David A. Harbour - Alive and well Message-ID: <854406.27015.qm@web52710.mail.re2.yahoo.com> hi, i don't know who reported that, but it is a rumor!!! david is alive and well!! nancy enid cemetery manager --- On Wed, 2/25/09, ken.hunter wrote: From: ken.hunter Subject: David A. Harbour To: enidcemetery at sbcglobal.net Date: Wednesday, February 25, 2009, 8:59 AM Hello... I am an amateur Telescope Maker and a on-line friend of David Harbour. It has been reported on-line that David has passed away and I am hoping this is not true but have no way of finding information about this other than requesting confirmation from you. David's wife Theresa and their two children are interred in the cemetery there. Can you confirm details of Mr. Harbours passing so that it can be correctly reported to his many on-line friends? Thanks so much. Ken Hunter Electronic Technician National Weather Service Lincoln, IL (217) 732-4029 X 382 From wkitty42 at windstream.net Tue Mar 3 03:31:10 2009 From: wkitty42 at windstream.net (waldo kitty) Date: Mon, 02 Mar 2009 13:31:10 -0500 Subject: [ATM] I am about to drill a hole in my aluminum tube In-Reply-To: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: <49AC25EE.1080605@windstream.net> Francis J. O'Reilly wrote: > I am about to drill an eyepiece hole in my aluminum tube, I would like a check on my arithmetic computations. > > The mirror is 12.25 inches in diameter. The focal length is 85 1/8 inches. The first surface of the mirror is 6 1/8 inches from the back end of the tube. The 90 inch long aluminum tube is somewhat oval, but not too bad. The diameter where I will put the eyepiece is 15 1/8 inches. The height of the two inch focuser is three inches. > > I come up with 81.75 inches from the back of the tube as the center point of the eyepiece hole. > > I would appreciate any thoughts on this matter. I made a bad mistake with a prior tube abd I would like to avoid any further probelms. > > Thank you. the easiest thing for this newbie to do was to plug your numbers into NEWT v3.0 and see how it came out... i had to guess and work at a couple of things (ie: focal ration, you gave length so i had to do the math), the tube's thickness and then the distance from the front of the tube to the focuser... this last one, focuser to front of tube, is what you are trying to calculate whereas NEWT uses it as a set input... in my toying around, i tend to place the focuser the same distance from the front of the tube as the mirror face is from the back of the tube... the result of this is that NEWT calcs the focuser hole to be 73.937 inches from the mirror face (first surface?)... that plus the mirror face to the back of the tube gives me 80.062 inches... that puts my result 1.688 inches shorter then yours and i don't have a clue where that difference may have come from... other guessed at factors were the actual focuser specs... you state 2 inch focuser which i assume is the focuser's inside diameter... you also say that it is 3 inches tall when racked all the way in... if i've done/read the below correctly, i allowed for another 1/2 inch of travel in... if i remove the 1/2 extra travel, the focuser hole moves 1/2 inch further away from the mirror face... this also shows that your tube length of 90 inches is a hair under 4 inches longer than necessary but i don't think that'll really be a problem ;) i have not messed with any eyepiece settings that come with NEWT and have not included anything related to them or baffles in the output below... so, anyway... here's what i came up with... dunno if it helps any or not... Specifications/Dimensions (w/ .5 inch focuser travel): Unit of Measure -------------- inch Primary Mirror Diameter ------ 12.25 Focal Length ----------------- 85.125 Focal Ratio ------------------ 6.949 Tube Inside Diameter --------- 15.125 Tube Thickness --------------- 0.1250 Focuser Height --------------- 3.0 Focuser Inside Diameter ------ 2.0 Focuser Extra Travel --------- 0.5 Focuser Camera Travel -------- 0.0 Diagonal Minor Axis ---------- 2.0 Diagonal Offset -------------- 0.0719 100% Illumination Diameter --- 0.4490 75% Illumination Diameter ---- 1.2794 Front Aperture Diameter ------ 13.444 Mirror Face to Focuser Hole -- 73.937 Focuser to Front End of Tube - 6.125 Mirror Face to Back of Tube -- 6.125 Tube Length ------------------ 86.187 Specifications/Dimensions (wo/ .5 inch focuser travel): Unit of Measure -------------- inch Primary Mirror Diameter ------ 12.25 Focal Length ----------------- 85.125 Focal Ratio ------------------ 6.949 Tube Inside Diameter --------- 15.125 Tube Thickness --------------- 0.1250 Focuser Height --------------- 3.0 Focuser Inside Diameter ------ 2.0 Focuser Extra Travel --------- 0.0 Focuser Camera Travel -------- 0.0 Diagonal Minor Axis ---------- 2.0 Diagonal Offset -------------- 0.0719 100% Illumination Diameter --- 0.5283 75% Illumination Diameter ---- 1.3117 Front Aperture Diameter ------ 13.482 Mirror Face to Focuser Hole -- 74.437 Focuser to Front End of Tube - 6.125 Mirror Face to Back of Tube -- 6.125 Tube Length ------------------ 86.687 Note: All positions measured from the back of the tube. - NOTE: NEW EMAIL ADDRESS!! _\/ (@@) Waldo Kitty, Waldo's Place USA __ooO_( )_Ooo_____________________ telnet://bbs.wpusa.dynip.com _|_____|_____|_____|_____|_____|_____ http://www.wpusa.dynip.com ____|_____|_____|_____|_____|_____|____ ftp://ftp.wpusa.dynip.com _|_Eat_SPAM_to_email_me!_YUM!__|_____ wkitty42 -at- windstream.net From rflrs at rcn.com Tue Mar 3 05:21:42 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Mon, 02 Mar 2009 15:21:42 -0500 Subject: [ATM] Split Corrector Refractor with a Littrow Objective Message-ID: <49AC3FD6.8090700@rcn.com> It has been suggested that perhaps the simplest doublet to build is the Littrow doublet, consisting of an isoconvex crown and mating planoconcave flint. Per volume, N-BK7 and N-F2 are among the cheapest of the Schott ECO optical glasses. When a Littrow is made using these glasses, and a split corrector is designed against it within certain constraints, the radii on the split corrector nearly match -- this can be tweaked some by adjusting relative thicknesses of the lenses away from nominal (including the Littrow lens thicknesses, as that affects the lateral color correction. By adjusting the focal length, one could set up prescription requirements for the corrector that nearly match OTS lenses. I chose a 3" planoconvex and a 2" isoconcave from Ross as a test case. I also selected f/15 to eliminate vignetting on a +/-21 mm field, while still using nearly all of the aperture of the corrector lenses. The result is (134.585 mm f/15): http://users.rcn.com/rflrs/Ptz11-54x.atm ATMOS input file http://users.rcn.com/rflrs/Ptz11-54x.len OSLO input file http://users.rcn.com/rflrs/Ptz11-54x.txt TEXT prescription http://users.rcn.com/rflrs/Ptz11-54x.zmx ZEMAX input file The Visual Strehl is quite regular, varying by about one in the fourth decimal place over the full field. From john_lynch2007 at yahoo.com Tue Mar 3 06:41:04 2009 From: john_lynch2007 at yahoo.com (John Lynch) Date: Mon, 2 Mar 2009 13:41:04 -0800 (PST) Subject: [ATM] I am about to drill a hole in my aluminum tube Message-ID: <346406.17767.qm@web110101.mail.gq1.yahoo.com> Jan, ? I think you mean "subtracted."? The focal plane, if 1" above the fully racked in focuser, has to remain a fixed distance from the mirror, i.e., the focal length.? Everything else must change to accomodate this.? Therefore, the distance from the mirror to the focuser hole should?be 1" shorter.? My result is 79.625." ? John --- On Mon, 3/2/09, Jan van Gastel wrote: From: Jan van Gastel Subject: Re: [ATM] I am about to drill a hole in my aluminum tube To: "Francis J. O'Reilly" , atm at atmlist.net Cc: "Dick Parker" Date: Monday, March 2, 2009, 1:37 AM Francis, Assuming that (a) 3" is the height of the fully racked-in focuser and (b) the focal point is at the outer end of that 3" focuser (for the moment, we correct this at the end), the distance from the focal plane to the center of the tube (optical axis) is 12.25/2+(15.125-12.25)/2+3=10.56". The vertical distance from the mirror face to the center of the focuser hole is: 85.125-10.56= 74.56". The vertical distance from the back of the tube to the center of the focuser hole is: 74.56+6.125 = 80.69". The real focal point will not be at the end of the fully racked in 3 inch focuser, so to this 80.69", the focuser in travel that you want, has to be added. If the focuser in travel is 1.06 inch (say, 1 inch) your calculations are correct. This is how I always do the calculations. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Francis J. O'Reilly" To: Cc: "Dick Parker" Sent: Monday, March 02, 2009 1:50 Subject: [ATM] I am about to drill a hole in my aluminum tube > I am about to drill an eyepiece hole in my aluminum tube, I would like a check on my arithmetic computations. > > The mirror is 12.25 inches in diameter. The focal length is 85 1/8 inches.. The first surface of the mirror is 6 1/8 inches from the back end of the tube. The 90 inch long aluminum tube is somewhat oval, but not too bad. The diameter where I will put the eyepiece is 15 1/8 inches. The height of the two inch focuser is three inches. > > I come up with 81.75 inches from the back of the tube as the center point of the eyepiece hole. > > I would appreciate any thoughts on this matter. I made a bad mistake with a prior tube abd I would like to avoid any further probelms. > > Thank you. > > Francis J. O'Reilly > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ From jhm.vangastel at ziggo.nl Tue Mar 3 07:29:14 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Mon, 2 Mar 2009 23:29:14 +0100 Subject: [ATM] I am about to drill a hole in my aluminum tube Message-ID: Yes, of course, I mean the in-travel has to be *subtracted*, not added. Stupid mistake! Sorry Francis. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: John Lynch To: Jan van Gastel Cc: ATMListserv Sent: Monday, March 02, 2009 22:41 Subject: Re: [ATM] I am about to drill a hole in my aluminum tube > Jan, > I think you mean "subtracted." The focal plane, if 1" above the fully > racked in > focuser, has to remain a fixed distance from the mirror, i.e., the >focal > length. Everything else must change to accomodate this. Therefore, the > distance from the mirror to the focuser hole should be 1" shorter. My > result is 79.625." John --- On Mon, 3/2/09, Jan van Gastel wrote: From: Jan van Gastel Subject: Re: [ATM] I am about to drill a hole in my aluminum tube To: "Francis J. O'Reilly" , atm at atmlist.net Cc: "Dick Parker" Date: Monday, March 2, 2009, 1:37 AM Francis, Assuming that (a) 3" is the height of the fully racked-in focuser and (b) the focal point is at the outer end of that 3" focuser (for the moment, we correct this at the end), the distance from the focal plane to the center of the tube (optical axis) is 12.25/2+(15.125-12.25)/2+3=10.56". The vertical distance from the mirror face to the center of the focuser hole is: 85.125-10.56= 74.56". The vertical distance from the back of the tube to the center of the focuser hole is: 74.56+6.125 = 80.69". The real focal point will not be at the end of the fully racked in 3 inch focuser, so to this 80.69", the focuser in travel that you want, has to be added. If the focuser in travel is 1.06 inch (say, 1 inch) your calculations are correct. This is how I always do the calculations. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Francis J. O'Reilly" To: Cc: "Dick Parker" Sent: Monday, March 02, 2009 1:50 Subject: [ATM] I am about to drill a hole in my aluminum tube > I am about to drill an eyepiece hole in my aluminum tube, I would like a check on my arithmetic computations. > > The mirror is 12.25 inches in diameter. The focal length is 85 1/8 inches. The first surface of the mirror is 6 1/8 inches from the back end of the tube. The 90 inch long aluminum tube is somewhat oval, but not too bad. The diameter where I will put the eyepiece is 15 1/8 inches. The height of the two inch focuser is three inches. > > I come up with 81.75 inches from the back of the tube as the center point of the eyepiece hole. > > I would appreciate any thoughts on this matter. I made a bad mistake with a prior tube abd I would like to avoid any further probelms. > > Thank you. > > Francis J. O'Reilly > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ------------------------------------------------------------ As of 10-01-2008 my email address has been changed to jhm.vangastel at ziggo.nl Will you be so kind as to use this address from now on? New webadress: http://members.ziggo.nl/jhm.vangastel/Astronomy Please, update your links Per 1-10-2008 is mijn emailadres gewijzigd in jhm.vangastel at ziggo.nl Wilt u zo goed zijn voortaan dit adres te gebruiken? Nieuw website adres: http://members.ziggo.nl/jhm.vangastel/Astronomy/ Wilt u een eventuele link aanpassen? ----------------------------------------------------------- ----- Original Message ----- From: "Jan van Gastel" To: "Francis J. O'Reilly" ; Cc: "Dick Parker" Sent: Monday, March 02, 2009 7:37 Subject: Re: [ATM] I am about to drill a hole in my aluminum tube > Francis, > > Assuming that (a) 3" is the height of the fully racked-in focuser and (b) > the focal point is at the outer end of that 3" focuser (for the moment, we > correct this at the end), the distance from the focal plane to the center > of the tube (optical axis) is 12.25/2+(15.125-12.25)/2+3=10.56". The > vertical distance from the mirror face to the center of the focuser hole > is: 85.125-10.56= 74.56". The vertical distance from the back of the tube > to the center of the focuser hole is: 74.56+6.125 = 80.69". The real focal > point will not be at the end of the fully racked in 3 inch focuser, so to > this 80.69", the focuser in travel that you want, has to be added. If the > focuser in travel is 1.06 inch (say, 1 inch) your calculations are > correct. This is how I always do the calculations. > > Jan > http://members.ziggo.nl/jhm.vangastel/Astronomy/ > > > > ----- Original Message ----- > From: "Francis J. O'Reilly" > To: > Cc: "Dick Parker" > Sent: Monday, March 02, 2009 1:50 > Subject: [ATM] I am about to drill a hole in my aluminum tube > > >>I am about to drill an eyepiece hole in my aluminum tube, I would like a >>check on my arithmetic computations. >> >> The mirror is 12.25 inches in diameter. The focal length is 85 1/8 >> inches. The first surface of the mirror is 6 1/8 inches from the back end >> of the tube. The 90 inch long aluminum tube is somewhat oval, but not too >> bad. The diameter where I will put the eyepiece is 15 1/8 inches. The >> height of the two inch focuser is three inches. >> >> I come up with 81.75 inches from the back of the tube as the center point >> of the eyepiece hole. >> >> I would appreciate any thoughts on this matter. I made a bad mistake with >> a prior tube abd I would like to avoid any further probelms. >> >> Thank you. >> >> Francis J. O'Reilly >> >> _______________________________________________ >> ATM mailing list http://www.atmlist.net/ > From davegran at ticon.net Tue Mar 3 12:47:56 2009 From: davegran at ticon.net (Dave Grandeffo) Date: Mon, 02 Mar 2009 21:47:56 -0600 Subject: [ATM] [Francis] I am about to drill a hole in my aluminum tube In-Reply-To: References: Message-ID: <49ACA86C.5030202@ticon.net> > Shane and Bob, > > I've already mounted the primary. It is pretty heavy and I really > don't have anyone at home to help me with it. I appreciate your > suggestion, It's just a little late I acted prematurely. > > Francis > Francis, Would it be possible to incorporate some spacer blocks into the interface between your primary support cell and its mounting? Or between the mounting and the tube? Then you could take your best shot at locating the focuser and use the spacer blocks for fine tuning. -- Dave Grandeffo From dlwebb at canit.se Tue Mar 3 18:38:49 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Tue, 3 Mar 2009 10:38:49 +0100 (MET) Subject: [ATM] mirror making - the biggest issue In-Reply-To: <006701c99a9b$264feb70$72efc250$@com> Message-ID: On Sun, 1 Mar 2009, Mel Bartels wrote: > Invariably the biggest issue in mirror making, particularly from those > starting on the journey, those isolated from others, is the grinding > strokes. I am pleased to report that this in-person inspection is working. On this end there is a newbie working one of Richard Schwartz's slumped 13" F/3 plate glass blanks, about 3/4" thick. Rather advanced newbie project! After some initial monitoring of his strokes, and one minor run-in with the mirror seizing to the tool (tool is my standard concrete construct, BTW), this mirror is about done with 400 SiC and is essentially perfectly spherical. My ~40 mm diameter ring spherometer has precision of 2 micron and detects no errors across the entire surface. It is currently almost completely free of any scratches or pits. We shall see how this continues, but it looks to me like this somewhat advanced newbie project will go to completion with good success. It seems not much in-person assistance is needed. A few minutes of occasional intervention guarantees a happy ending. Dominic From dlwebb at canit.se Tue Mar 3 18:48:48 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Tue, 3 Mar 2009 10:48:48 +0100 (MET) Subject: [ATM] 8 inch f/5 too fast? In-Reply-To: Message-ID: My first scope was an 8" F/8. I had no idea what I was doing, and I was quite young. I figured out what ROC was on my own and made a compass to draw an arc onto a piece of cardboard. I cut this out and used this as my guide for when the sagitta had been reached. This trick worked out great. ROC on final mirror is within one inch, by optical tests. All newts have coma, such is life. An F/5 will perform wonderfully and it is not bad F/ratio to progress to a classical Cassegrain if you want. If you want more magnification, a 2X Barlow is another option. Dominic From jhm.vangastel at ziggo.nl Tue Mar 3 18:52:49 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Tue, 3 Mar 2009 10:52:49 +0100 Subject: [ATM] polish how long? References: <354982.85035.qm@web59203.mail.re1.yahoo.com> <1529808C45B8446A86FEF9E8808F5CD1@niks03981037eb> <001001c99861$ff8f4980$8f78fea9@amd> Message-ID: <289060812587416A88F85FF81BBB7A56@niks03981037eb> For the first time my final grinding powder was 3 mu, for less polishing time. Could someone give an indication (I know I will have to test, but an indication would be nice if possible) about how long polishing will take on a 8" f/4, with CEO, after an hour 3 mu grinding? Sharpie test showed a spherical mirror and and nice equally ground surface at the end of 3 mu. There's good contact with polishing tool and mirror (already did half an hour MOT). Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ From foreilly at verizon.net Tue Mar 3 21:13:23 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Tue, 03 Mar 2009 07:13:23 -0500 Subject: [ATM] polish how long? References: <354982.85035.qm@web59203.mail.re1.yahoo.com> <1529808C45B8446A86FEF9E8808F5CD1@niks03981037eb> <001001c99861$ff8f4980$8f78fea9@amd> <289060812587416A88F85FF81BBB7A56@niks03981037eb> Message-ID: Jan, I usually allow about two hours per inch of aperture. Others will disagree, but I don't like any grey whatsoever. I use a high intensity light to check the mirror, not a laser. Shine it on the surface of the glass and look closely, right now you will see tyhe light on the surface and very little light will pass through. When you look at the cleaned surface of the mirror and no light stays on the surface, anywhere, it all goes through, you are done polishing. Francis From jhm.vangastel at ziggo.nl Tue Mar 3 23:43:49 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Tue, 3 Mar 2009 15:43:49 +0100 Subject: [ATM] polish how long? References: <354982.85035.qm@web59203.mail.re1.yahoo.com> <1529808C45B8446A86FEF9E8808F5CD1@niks03981037eb> <001001c99861$ff8f4980$8f78fea9@amd> <289060812587416A88F85FF81BBB7A56@niks03981037eb> Message-ID: <48A6427C70AC4EB788FEAF4EAC0A7EED@niks03981037eb> That would be 16 hours of polishing. I polished 10-12 hours on each of my two 12 inchers two years ago and I shought it would be faster, because I already ground with 3 mu grit. I hope it will not last 16 hours. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Francis J. O'Reilly" To: "Jan van Gastel" ; Sent: Tuesday, March 03, 2009 13:13 Subject: Re: [ATM] polish how long? > Jan, > > I usually allow about two hours per inch of aperture. Others will > disagree, but I don't like any grey whatsoever. > > I use a high intensity light to check the mirror, not a laser. Shine it on > the surface of the glass and look closely, right now you will see tyhe > light on the surface and very little light will pass through. When you > look at the cleaned surface of the mirror and no light stays on the > surface, anywhere, it all goes through, you are done polishing. > > Francis From hermit at outofoptions.org Wed Mar 4 00:23:46 2009 From: hermit at outofoptions.org (hermit) Date: Tue, 03 Mar 2009 10:23:46 -0500 Subject: [ATM] polish how long? In-Reply-To: <48A6427C70AC4EB788FEAF4EAC0A7EED@niks03981037eb> References: <354982.85035.qm@web59203.mail.re1.yahoo.com> <1529808C45B8446A86FEF9E8808F5CD1@niks03981037eb> <001001c99861$ff8f4980$8f78fea9@amd> <289060812587416A88F85FF81BBB7A56@niks03981037eb> <48A6427C70AC4EB788FEAF4EAC0A7EED@niks03981037eb> Message-ID: <49AD4B82.7010400@outofoptions.org> I think it is Mel that has pointed out pressure is key here. Plus you said it is a fast mirror if I remember correctly? You have a lot to 'figure' away so keep that in mind too. Ken Lowther Jan van Gastel wrote: > That would be 16 hours of polishing. I polished 10-12 hours on each of > my two 12 inchers two years ago and I shought it would be faster, > because I already ground with 3 mu grit. I hope it will not last 16 > hours. > > Jan > http://members.ziggo.nl/jhm.vangastel/Astronomy/ > > > > > > ----- Original Message ----- From: "Francis J. O'Reilly" > > To: "Jan van Gastel" ; > Sent: Tuesday, March 03, 2009 13:13 > Subject: Re: [ATM] polish how long? > > >> Jan, >> >> I usually allow about two hours per inch of aperture. Others will >> disagree, but I don't like any grey whatsoever. >> >> I use a high intensity light to check the mirror, not a laser. Shine >> it on the surface of the glass and look closely, right now you will >> see tyhe light on the surface and very little light will pass >> through. When you look at the cleaned surface of the mirror and no >> light stays on the surface, anywhere, it all goes through, you are >> done polishing. >> >> Francis > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From jhm.vangastel at ziggo.nl Wed Mar 4 01:20:59 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Tue, 3 Mar 2009 17:20:59 +0100 Subject: [ATM] polish how long? References: <354982.85035.qm@web59203.mail.re1.yahoo.com> <1529808C45B8446A86FEF9E8808F5CD1@niks03981037eb> <001001c99861$ff8f4980$8f78fea9@amd> <289060812587416A88F85FF81BBB7A56@niks03981037eb> Message-ID: <89D91D86DACE45889330A08065E18D4A@niks03981037eb> Francis, I do this with a laser, in the dark. Is the kind of light you use (much) more critical? Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Francis J. O'Reilly" To: "Jan van Gastel" ; Sent: Tuesday, March 03, 2009 13:13 Subject: Re: [ATM] polish how long? > Jan, > > I usually allow about two hours per inch of aperture. Others will > disagree, but I don't like any grey whatsoever. > > I use a high intensity light to check the mirror, not a laser. Shine it on > the surface of the glass and look closely, right now you will see tyhe > light on the surface and very little light will pass through. When you > look at the cleaned surface of the mirror and no light stays on the > surface, anywhere, it all goes through, you are done polishing. > > Francis From tcohen at blakeglobal.com Wed Mar 4 04:01:02 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Tue, 3 Mar 2009 11:01:02 -0800 Subject: [ATM] astigmatism question Message-ID: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL> I'm working to get spherical and I've detected some minor astigmatism that I believe is actually in the mirror and not in my test setup. My question is: if henceforth I use the correct technique such that no additional astigmatic aberration is applied to the glass, will the existing astigmatism tend to clear up over time? Or, does this type of aberration become amplified if not cured early on in polishing? The question is to help me decide how aggressively I need to address the problem. I think I have the understanding necessary to interpret and apply the proper correction, but would prefer (if feasible) to address this with further polishing action and a proper technique, without resorting to asymmetrical stroking/pressure. From atmpob at yahoo.com Wed Mar 4 05:40:08 2009 From: atmpob at yahoo.com (Dale Eason) Date: Tue, 3 Mar 2009 12:40:08 -0800 (PST) Subject: [ATM] astigmatism question In-Reply-To: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL> Message-ID: <974920.36609.qm@web54501.mail.re2.yahoo.com> Although I don't know the answer. If I was one that did know I think I would first want to know how you detected the astig. Just to make sure that it is real and that you truely know how to detect it. So just for our education can you tell us how you detected it? Dale Eason --- On Tue, 3/3/09, Ted Cohen wrote: > From: Ted Cohen > Subject: [ATM] astigmatism question > To: atm at atmlist.net > Date: Tuesday, March 3, 2009, 1:01 PM > I'm working to get spherical and I've detected some > minor astigmatism that I > believe is actually in the mirror and not in my test setup. > My question is: > if henceforth I use the correct technique such that no > additional astigmatic > aberration is applied to the glass, will the existing > astigmatism tend to > clear up over time? Or, does this type of aberration become > amplified if not > cured early on in polishing? The question is to help me > decide how > aggressively I need to address the problem. I think I have > the understanding > necessary to interpret and apply the proper correction, but > would prefer (if > feasible) to address this with further polishing action and > a proper > technique, without resorting to asymmetrical > stroking/pressure. > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From foreilly at bestweb.net Wed Mar 4 06:04:31 2009 From: foreilly at bestweb.net (Francis J. O'Reilly) Date: Tue, 3 Mar 2009 16:04:31 -0500 Subject: [ATM] Newt spreadsheet] References: <49AD857F.8020109@hetnet.nl> Message-ID: Arjan and all others,, Thank you very much for your kind assistance with the issue of drilling my tube. Making the decision as to where to drill the hole is harder than making a decision to get married. Francis From tcohen at blakeglobal.com Wed Mar 4 07:27:48 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Tue, 3 Mar 2009 14:27:48 -0800 Subject: [ATM] astigmatism question In-Reply-To: <974920.36609.qm@web54501.mail.re2.yahoo.com> References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL> <974920.36609.qm@web54501.mail.re2.yahoo.com> Message-ID: <73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> Re: So just for our education can you tell us how you detected it? Yes, I detected it using a Ronchi grating, which shows an asymmetrical bending to the diffraction pattern when placed just inside the center of curvature. My grating is 150 lines per inch and the mirror is F4. There are nine or ten lines silhouetted over the aperture. The two centermost lines, which straddle either side of the mirror's axis both bend in the same direction creating an unequal number of lines on each side. In the outer zones, the problem is absent. However, in the inner region within the 70% zone, there are 5 lines on one side of the axis, and four lines on the other side. Given the overall surface, which is an oblate spheroid, with a slight depression in the 65%-85% zone, the bending is consistent with an excessive deepening on one side of the 0% - 50% zone. The astigmatic zone is perpendicular to the gravity vector, and I'm pretty sure (but not yet positively sure) that it is actually in the glass and not a result of the horizontal strap testing mount. From jack.swaton at starryhost.com Wed Mar 4 07:19:34 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Tue, 3 Mar 2009 14:19:34 -0800 Subject: [ATM] Newt spreadsheet] In-Reply-To: References: <49AD857F.8020109@hetnet.nl> Message-ID: Tell us this is a rhetorical observation, no? Are congratulations due??? ;-0 Jack Swaton www.starryhost.com -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Francis J. O'Reilly Sent: Tuesday, March 03, 2009 1:05 PM To: Arjan te Marvelde (hetnet) Cc: atm at atmlist.net Subject: Re: [ATM] Newt spreadsheet] Arjan and all others,, Thank you very much for your kind assistance with the issue of drilling my tube. Making the decision as to where to drill the hole is harder than making a decision to get married. Francis _______________________________________________ ATM mailing list http://www.atmlist.net/ From daze39 at earthlink.net Wed Mar 4 07:29:07 2009 From: daze39 at earthlink.net (David Weinshenker) Date: Tue, 03 Mar 2009 14:29:07 -0800 Subject: [ATM] astigmatism question In-Reply-To: <73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL> <974920.36609.qm@web54501.mail.re2.yahoo.com> <73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> Message-ID: <49ADAF33.40100@earthlink.net> Ted Cohen wrote: > Re: So just for our education can you tell us how you detected it? > > Yes, I detected it using a Ronchi grating, which shows an asymmetrical > bending to the diffraction pattern when placed just inside the center of > curvature. My grating is 150 lines per inch and the mirror is F4. There are > nine or ten lines silhouetted over the aperture. The two centermost lines, > which straddle either side of the mirror's axis both bend in the same > direction creating an unequal number of lines on each side. In the outer > zones, the problem is absent. However, in the inner region within the 70% > zone, there are 5 lines on one side of the axis, and four lines on the other > side. Given the overall surface, which is an oblate spheroid, with a slight > depression in the 65%-85% zone, the bending is consistent with an excessive > deepening on one side of the 0% - 50% zone. The astigmatic zone is > perpendicular to the gravity vector, and I'm pretty sure (but not yet > positively sure) that it is actually in the glass and not a result of the > horizontal strap testing mount. The standard method of testing this last point would be to repeat the test with the glass turned to several different positions, to see if the anomaly is consistent in its position on the glass (rather than relative to the support). For example, turn the glass 180 degrees and see if you now observe more lines on the other side of the axis. -dave w From hermit at outofoptions.org Wed Mar 4 09:10:29 2009 From: hermit at outofoptions.org (hermit) Date: Tue, 03 Mar 2009 19:10:29 -0500 Subject: [ATM] Newt spreadsheet] In-Reply-To: References: <49AD857F.8020109@hetnet.nl> Message-ID: <49ADC6F5.7060504@outofoptions.org> You can always borrow some hands and mock up a dry run outside the tube if you are that concerned about it. Ken Lowther Francis J. O'Reilly wrote: > Arjan and all others,, > > Thank you very much for your kind assistance with the issue of > drilling my tube. Making the decision as to where to drill the hole is > harder than making a decision to get married. > > Francis > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From atmpob at yahoo.com Wed Mar 4 09:41:08 2009 From: atmpob at yahoo.com (Dale Eason) Date: Tue, 3 Mar 2009 16:41:08 -0800 (PST) Subject: [ATM] astigmatism question In-Reply-To: <73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> Message-ID: <324318.7013.qm@web54504.mail.re2.yahoo.com> It would be interesting to see a picture of that. Do you have the capability to take one? They can be uploaded into the atmlist upload area and then linked into an email post. What you describe does not match what I usually see as astig in ronchi images. It is a defect of some kind but perhaps not of astig. I wonder what others think. For something to show up in Ronchi images like that I think it might be large and may need more than the usually methods of removal but that is a guess. I hope you can get a picture of it. Dale Eason --- On Tue, 3/3/09, Ted Cohen wrote: > From: Ted Cohen > Subject: Re: [ATM] astigmatism question > To: atm at atmlist.net > Date: Tuesday, March 3, 2009, 4:27 PM > Re: So just for our education can you tell us how you > detected it? > > Yes, I detected it using a Ronchi grating, which shows an > asymmetrical > bending to the diffraction pattern when placed just inside > the center of > curvature. My grating is 150 lines per inch and the mirror > is F4. There are > nine or ten lines silhouetted over the aperture. The two > centermost lines, > which straddle either side of the mirror's axis both > bend in the same > direction creating an unequal number of lines on each side. > In the outer > zones, the problem is absent. However, in the inner region > within the 70% > zone, there are 5 lines on one side of the axis, and four > lines on the other > side. Given the overall surface, which is an oblate > spheroid, with a slight > depression in the 65%-85% zone, the bending is consistent > with an excessive > deepening on one side of the 0% - 50% zone. The astigmatic > zone is > perpendicular to the gravity vector, and I'm pretty > sure (but not yet > positively sure) that it is actually in the glass and not a > result of the > horizontal strap testing mount. > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From holmmarkd at gmail.com Wed Mar 4 09:44:01 2009 From: holmmarkd at gmail.com (Mark Holm) Date: Tue, 03 Mar 2009 19:44:01 -0500 Subject: [ATM] astigmatism question In-Reply-To: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL> References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL> Message-ID: <49ADCED1.20000@gmail.com> I'm not an expert on this, but since I have read a good number of messages, over the years, on this list about astigmatism troubles, I think I can make a couple of points with reasonable assurance of being correct. 1. The Ronchi and Foucault tests are not terribly sensitive to astigmatism. If you can see it, it is probably pretty bad. 2. Astigmatism probably results from a. Bad glass ( not flat enough back, bad annealing, very bad wedge), b. Bad support during grinding/polishing, c. Bad support during testing. If it was b. and you didn't change the support significantly from grinding to polishing, it seems likely that you ground it in. This is consistent with a. which says that the magnitude is probably larger than you think. c. is a real possibility, but if you have convinced yourself that it rotates with the mirror, perhaps is can be put lower down the scale of possibilities. My guess is that, after correcting the support (or glass) issue, you will be best served by going back to the last grade or two of fine grinding. I know that is a hard pill to swallow, but it is going to take an awfully long time to polish out something you ground in. Also, you ability to measure it is limited: better to have a setup that naturally eliminates it than trying to reduce it below measureability. Can you tell us about your glass: Plate, Pyrex, etc. source, thickness, annealing, back flatness, wedge? How about your back support during grinding and polishing? Also, frequency of rotation during grinding and polishing. Have you been rotating tool and mirror in opposite directions? Have you been rotating them by a reasonably random amount and not by an amount that would be likely to add up to 90 or 180 degrees repeatedly? -- Mark Holm markholm at verizon.net holmmarkd at gmail.com From gfbrandenburg at yahoo.com Wed Mar 4 10:05:49 2009 From: gfbrandenburg at yahoo.com (Guy Brandenburg) Date: Tue, 3 Mar 2009 17:05:49 -0800 (PST) Subject: [ATM] Newt spreadsheet] In-Reply-To: Message-ID: <401126.23229.qm@web111511.mail.gq1.yahoo.com> Francis, I respectfully submit that I think you are doing it backwards. Drill the main hole for the focuser and install that wherever you guess it should go, then make a jig so that you can move the primary backwards and forwards in the tube until you can focus on the moon, a planet, or whatever. (Not on the house across the street! You need to focus at infinity.) Then mark where the primary should go, drill its little holes, and you are done. I have done the calculations that various folks on here have cited, numerous times for numerous scopes, and I think that the formulas are just plain wrong. Nothing ever came out correctly. (I think I know my way around a calculator and a formula or two.) Or else, where I think the focal plane in my eyepieces should be, ain't it. And, anyway, eyepieces can vary by a LOT. I understand, Francis, that you put in the primary first; but it's much easier to move the primary than to move the focuser. A little bit of thought will allow you to come up with a suitable jig for holding the primary temporarily in place. What I generally do, after I've done the calculations (which won't work), is to use is some shims between the edges of the primary holder and the sides of the tube to hold it all in place temporarily, and if the position ain't right, I just tap things loose with a hammer or mallet or 2 by 4, and then either shove the primary up or down the tube a bit, and repeat. All of this is a bit easier with a partner, but it's not required. That's my 2 cents. Good luck. Guy Brandenburg, Washington, DC My home page on astronomy, mathematics, education: http://home.earthlink.net/~gfbranden/GFB_Home_Page.html or else http://tinyurl.com/r6fh2 ============================= "Education isn't rocket science. It's much, much harder." (Author unknown) --- On Tue, 3/3/09, Francis J. O'Reilly wrote: > From: Francis J. O'Reilly > Subject: Re: [ATM] Newt spreadsheet] > To: "Arjan te Marvelde (hetnet)" > Cc: atm at atmlist.net > Date: Tuesday, March 3, 2009, 4:04 PM > Arjan and all others,, > > Thank you very much for your kind assistance with the issue > of drilling my tube. Making the decision as to where to > drill the hole is harder than making a decision to get > married. > > Francis > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From tcohen at blakeglobal.com Wed Mar 4 10:19:00 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Tue, 3 Mar 2009 17:19:00 -0800 Subject: [ATM] astigmatism question In-Reply-To: <49ADCED1.20000@gmail.com> References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL> <49ADCED1.20000@gmail.com> Message-ID: The astigmatism showed up rather suddenly and appears to be of similar magnitude with the remaining spherical aberration. I believe that as I approach spherical and start getting more sensitive readings with the Ronchi grating approaching the COC, the problem that was previously drowned out by spherical aberration is now becoming apparent. I don't see the astigmatism unless the grating is very close to the center of curvature. Ted Cohen Joseph J. Blake and Associates, Inc. One Concord Center 2300 Clayton Road, Suite 1300 Concord, CA 94520 925-356-0950 ext. 112 (phone) 925-356-0956 (fax) tcohen at blakeglobal.com www.blakeglobal.com -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Mark Holm Sent: Tuesday, March 03, 2009 4:44 PM To: atm at atmlist.net Subject: Re: [ATM] astigmatism question I'm not an expert on this, but since I have read a good number of messages, over the years, on this list about astigmatism troubles, I think I can make a couple of points with reasonable assurance of being correct. 1. The Ronchi and Foucault tests are not terribly sensitive to astigmatism. If you can see it, it is probably pretty bad. 2. Astigmatism probably results from a. Bad glass ( not flat enough back, bad annealing, very bad wedge), b. Bad support during grinding/polishing, c. Bad support during testing. If it was b. and you didn't change the support significantly from grinding to polishing, it seems likely that you ground it in. This is consistent with a. which says that the magnitude is probably larger than you think. c. is a real possibility, but if you have convinced yourself that it rotates with the mirror, perhaps is can be put lower down the scale of possibilities. My guess is that, after correcting the support (or glass) issue, you will be best served by going back to the last grade or two of fine grinding. I know that is a hard pill to swallow, but it is going to take an awfully long time to polish out something you ground in. Also, you ability to measure it is limited: better to have a setup that naturally eliminates it than trying to reduce it below measureability. Can you tell us about your glass: Plate, Pyrex, etc. source, thickness, annealing, back flatness, wedge? How about your back support during grinding and polishing? Also, frequency of rotation during grinding and polishing. Have you been rotating tool and mirror in opposite directions? Have you been rotating them by a reasonably random amount and not by an amount that would be likely to add up to 90 or 180 degrees repeatedly? -- Mark Holm markholm at verizon.net holmmarkd at gmail.com _______________________________________________ ATM mailing list http://www.atmlist.net/ From gfbrandenburg at yahoo.com Wed Mar 4 10:19:24 2009 From: gfbrandenburg at yahoo.com (Guy Brandenburg) Date: Tue, 3 Mar 2009 17:19:24 -0800 (PST) Subject: [ATM] polish how long? In-Reply-To: <289060812587416A88F85FF81BBB7A56@niks03981037eb> Message-ID: <137686.82066.qm@web111513.mail.gq1.yahoo.com> I think the most objective way to see if a mirror is well and truly polished is to use a little cheap hand-held 60 x illuminated microscope. Here in the US, Radio Shack sells them for $10. Don't know if there's something similar in the Netherlands. If you can see ANY grain or tiny pits whatsoever on your mirror with the little microscope, then you are not finished polishing. Guy From optical_stargazer at yahoo.com Wed Mar 4 10:41:50 2009 From: optical_stargazer at yahoo.com (Rick M) Date: Tue, 3 Mar 2009 17:41:50 -0800 (PST) Subject: [ATM] David A. Harbour - Alive and well In-Reply-To: <854406.27015.qm@web52710.mail.re2.yahoo.com> Message-ID: <505026.8373.qm@web31303.mail.mud.yahoo.com> Rick M http://groups.yahoo.com/group/AllAstronomyAllTheTime/ I am very glad to hear that Ken, Thank you. my astronomy & a.t.m. site http://www.geocities.com/optical_stargazer __________________________________________________________________ Yahoo! Canada Toolbar: Search from anywhere on the web, and bookmark your favourite sites. Download it now at http://ca.toolbar.yahoo.com. From foreilly at bestweb.net Wed Mar 4 10:54:20 2009 From: foreilly at bestweb.net (foreilly at bestweb.net) Date: Tue, 3 Mar 2009 20:54:20 -0500 (EST) Subject: [ATM] Newt spreadsheet] In-Reply-To: References: <49AD857F.8020109@hetnet.nl> Message-ID: <827d65c5c9425fa67d90b908038918cb.squirrel@webmail2.bestweb.net> Thank you Jack. I was divorced after twenty-six years and seven children. I then remarried three years ago.The attendant aggravation?took a chunk of time out of my telescope making life.I am back now.Francis > Tell us this is a rhetorical observation, no? Are congratulations due??? > > ;-0 > Jack Swaton > www.starryhost.com > > -----Original Message----- > From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf > Of > Francis J. O'Reilly > Sent: Tuesday, March 03, 2009 1:05 PM > To: Arjan te Marvelde (hetnet) > Cc: atm at atmlist.net > Subject: Re: [ATM] Newt spreadsheet] > > Arjan and all others,, > > Thank you very much for your kind assistance with the issue of drilling my > tube. Making the decision as to where to drill the hole is harder than > making a decision to get married. > > Francis > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > From don.surles at verizon.net Wed Mar 4 11:28:48 2009 From: don.surles at verizon.net (Don Surles) Date: Tue, 03 Mar 2009 20:28:48 -0600 (CST) Subject: [ATM] Newt spreadsheet] Message-ID: <1261680191.2999231236133728581.JavaMail.javamailuser@localhost> All...my 2 cents worth...i too learned the hard way to put the focuser in first. As for moving/adjusting the primary i always use a plywood mirror cell and put a 1/4-20 T-nut in the center of the rear element of the mirror cell. I then screw a 6-8 inch bolt into the 1/4-20 T-nut so that I can grab the bolt to move the primary up/down the tube whilst i am focusing on something at infinity...say a water tower at least a mile away. And I try to use a normal eyepiece...a 20-30mm plossel. When i find a place where the point of focus is about 1/2 the rack of the focuser i measure the distance from the rear of the tube to the mirror cell, disassemble the scope, go home and install the primary properly. Good luck. Oh, I have a scope with an extra set of holes in the tube. Don... On Tue, Mar 3, 2009 at 8:05 PM, Guy Brandenburg wrote: > Francis, I respectfully submit that I think you are doing it backwards. Drill the main hole for the focuser and install that wherever you guess it should go, then make a jig so that you can move the primary backwards and forwards in the tube until you can focus on the moon, a planet, or whatever. (Not on the house across the street! You need to focus at infinity.) Then mark where the primary should go, drill its little holes, and you are done. I have done the calculations that various folks on here have cited, numerous times for numerous scopes, and I think that the formulas are just plain wrong. Nothing ever came out correctly. (I think I know my way around a calculator and a formula or two.) Or else, where I think the focal plane in my eyepieces should be, ain't it. And, anyway, eyepieces can vary by a LOT. I understand, Francis, that you put in the primary first; but it's much easier to move the primary than to move the focuser. A little bit of thought will allow you to come up with a suitable jig for holding the primary temporarily in place. What I generally do, after I've done the calculations (which won't work), is to use is some shims between the edges of the primary holder and the sides of the tube to hold it all in place temporarily, and if the position ain't right, I just tap things loose with a hammer or mallet or 2 by 4, and then either shove the primary up or down the tube a bit, and repeat. All of this is a bit easier with a partner, but it's not required. That's my 2 cents. Good luck. Guy Brandenburg, Washington, DC My home page on astronomy, mathematics, education: http://home.earthlink.net/~gfbranden/GFB_Home_Page.html ? or else http://tinyurl.com/r6fh2 ? ============================= "Education isn't rocket science. It's much, much harder." (Author unknown) --- On Tue, 3/3/09, Francis J. O'Reilly ? > wrote: > From: Francis J. O'Reilly ? > > Subject: Re: [ATM] Newt spreadsheet] > To: "Arjan te Marvelde (hetnet)" ? > > > Cc: atm at atmlist.net ? > Date: Tuesday, March 3, 2009, 4:04 PM > Arjan and all others,, > > Thank you very much for your kind assistance with the issue > of drilling my tube. Making the decision as to where to > drill the hole is harder than making a decision to get > married. > > Francis > _______________________________________________ > ATM mailing list http://www.atmlist.net/ ? > ????? _______________________________________________ ATM mailing list http://www.atmlist.net/ ? From shane at ct-astronomer.com Wed Mar 4 11:31:06 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Tue, 3 Mar 2009 21:31:06 -0500 Subject: [ATM] Overlooked value of an RFT / Short F Ratio Newt Message-ID: <529F9DA5-7958-428D-AD13-E8901329DF0A@ct-astronomer.com> Since the primary optical issue of a short focal ratio Newtonian is coma, the best way to avoid coma is to use high power. This ensures that the image under focus is close to the optical axis, minimizing coma. This is opposite the traditional thought that a smallish short focal ratio Newtonian is best used for wide-field viewing only. Of course, the issues with high power observing in this type of telescope include quality of optics (a little harder to achieve in short focal ratios), larger secondary obstruction, and very short FL eyepieces required... but none of these are significant obstacles in a high quality image, as they are all achievable through careful figuring, reasonable secondary size, and modern eyepieces. I kind of came across this thought because I'm finishing up an 8" f4.2 paraboloid. I've already got 2 8" f5 scopes which are really wide enough in terms of real FOV, so maybe I'll make the f4.2 a planetary scope. Maybe a small secondary, and TeleVue Powermate 5x or something. Anyway, another winter... another mirror!!! best wishes, Shane LaPierre From rmay at nethere.com Wed Mar 4 11:39:37 2009 From: rmay at nethere.com (Bob May) Date: Tue, 3 Mar 2009 18:39:37 -0800 Subject: [ATM] 8 inch f/5 too fast? References: <49ABFCE8.5010901@gmail.com> Message-ID: <003101c99c72$788d49e0$8f78fea9@amd> A F5 will do fine, especially as a first telescope for all of the larger things in the sky. You won't be doing too well with it as a planetary scope tho as you won't be getting that much magnification. It does give you a definite choice for a second scope, one being of at least F10 which will be a lot better for doing planetary work. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Wed Mar 4 11:56:43 2009 From: rmay at nethere.com (Bob May) Date: Tue, 3 Mar 2009 18:56:43 -0800 Subject: [ATM] [Francis] I am about to drill a hole in my aluminum tube References: <49ACA86C.5030202@ticon.net> Message-ID: <003b01c99c74$da1ad220$8f78fea9@amd> The spacer bolocks idea is probably the best way to do this, especially if the primary needs to go towards the back a bit. I always put 3 blocks on the tube and mount the mirror cell with bolts that go up the tube. This allows me to remove the mirror without changing the position of the mirror when it needs to be cleaned. When you mount the mirror cell with screws in from the side, you can never be able to put the mirror back in the same place as it came out of as well as the cell sliding about and causing a constant realigning of the telescope. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Wed Mar 4 12:11:04 2009 From: rmay at nethere.com (Bob May) Date: Tue, 3 Mar 2009 19:11:04 -0800 Subject: [ATM] astigmatism question References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL><974920.36609.qm@web54501.mail.re2.yahoo.com> <73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> Message-ID: <005a01c99c77$47d5b940$8f78fea9@amd> Testing a spherical mirror for astigmatism is best done in my opinion by bringing the grating near the ROC and getting it to where there is one band spreading across almost half the mirror's width. Astig will show up as an S shaped line rather than a stright one. This will depend upon the angle of the astigmatism relative to the grating. I've seen lines that have done a full 180 degree reveersal of direction from the edge to the center! As you polish the glass, make sure that you keep turning the glass on the bottom to equalize the high spots. If you do the polishing MOT then make sure that the mirror keeps turning about on top of the tool and that the strokes go across the tool in differtn driections. FWIW, to get the astig. out of an average 1/2" thick piece of glass 13" in diameter, the glass, sitting on the table, had to be turned every minute by about 30 deg. to avoide the problem and it took a while to get the astig out taht was done by one session of polishing. The glass was a lens for a LH scope. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From wa4guu at verizon.net Wed Mar 4 12:27:25 2009 From: wa4guu at verizon.net (Jerry) Date: Tue, 03 Mar 2009 22:27:25 -0500 Subject: [ATM] Newt spreadsheet] In-Reply-To: Message-ID: <73DB468FDAA34E75B931EAC1807BD0C6@D85SJB21> Don't forget that the proper positioning and collimation of the secondary will affect the location of the focus relative to the top of the focuser. A little displacement of the diagonal along and across the optical axis will add or subtract the focal distance from the main tubes axis. Even when placing the focuser and diagonal first there is still some chance for error in placing the primary mirror if you don't properly align the diagonal first. Congratulations on the marriage Francis. Jerry -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Francis J. O'Reilly Sent: Tuesday, March 03, 2009 4:05 PM To: Arjan te Marvelde (hetnet) Cc: atm at atmlist.net Subject: Re: [ATM] Newt spreadsheet] Arjan and all others,, Thank you very much for your kind assistance with the issue of drilling my tube. Making the decision as to where to drill the hole is harder than making a decision to get married. Francis _______________________________________________ ATM mailing list http://www.atmlist.net/ From wkitty42 at windstream.net Wed Mar 4 15:11:25 2009 From: wkitty42 at windstream.net (waldo kitty) Date: Wed, 04 Mar 2009 01:11:25 -0500 Subject: [ATM] Newt spreadsheet] In-Reply-To: References: <49AD857F.8020109@hetnet.nl> Message-ID: <49AE1B8D.4080801@windstream.net> while i fully understand the complexities of both, and having been married before, i can only say "i wish!" :P Francis J. O'Reilly wrote: > Arjan and all others,, > > Thank you very much for your kind assistance with the issue of drilling > my tube. Making the decision as to where to drill the hole is harder > than making a decision to get married. -- NOTE: NEW EMAIL ADDRESS!! _\/ (@@) Waldo Kitty, Waldo's Place USA __ooO_( )_Ooo_____________________ telnet://bbs.wpusa.dynip.com _|_____|_____|_____|_____|_____|_____ http://www.wpusa.dynip.com ____|_____|_____|_____|_____|_____|____ ftp://ftp.wpusa.dynip.com _|_Eat_SPAM_to_email_me!_YUM!__|_____ wkitty42 -at- windstream.net From wkitty42 at windstream.net Wed Mar 4 15:13:32 2009 From: wkitty42 at windstream.net (waldo kitty) Date: Wed, 04 Mar 2009 01:13:32 -0500 Subject: [ATM] astigmatism question In-Reply-To: <73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL> <974920.36609.qm@web54501.mail.re2.yahoo.com> <73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> Message-ID: <49AE1C0C.7040509@windstream.net> what happens to those lines if you simply rotate the mirror without changing anything else? make sure to give some time to allow for hand/body heat to disapate after handling the mirror for the rotation ;) Ted Cohen wrote: > Re: So just for our education can you tell us how you detected it? > > Yes, I detected it using a Ronchi grating, which shows an asymmetrical > bending to the diffraction pattern when placed just inside the center of > curvature. My grating is 150 lines per inch and the mirror is F4. There are > nine or ten lines silhouetted over the aperture. The two centermost lines, > which straddle either side of the mirror's axis both bend in the same > direction creating an unequal number of lines on each side. In the outer > zones, the problem is absent. However, in the inner region within the 70% > zone, there are 5 lines on one side of the axis, and four lines on the other > side. Given the overall surface, which is an oblate spheroid, with a slight > depression in the 65%-85% zone, the bending is consistent with an excessive > deepening on one side of the 0% - 50% zone. The astigmatic zone is > perpendicular to the gravity vector, and I'm pretty sure (but not yet > positively sure) that it is actually in the glass and not a result of the > horizontal strap testing mount. -- NOTE: NEW EMAIL ADDRESS!! _\/ (@@) Waldo Kitty, Waldo's Place USA __ooO_( )_Ooo_____________________ telnet://bbs.wpusa.dynip.com _|_____|_____|_____|_____|_____|_____ http://www.wpusa.dynip.com ____|_____|_____|_____|_____|_____|____ ftp://ftp.wpusa.dynip.com _|_Eat_SPAM_to_email_me!_YUM!__|_____ wkitty42 -at- windstream.net From vladimir.galogaza1 at zg.t-com.hr Wed Mar 4 18:26:29 2009 From: vladimir.galogaza1 at zg.t-com.hr (Vladimir Galogaza) Date: Wed, 4 Mar 2009 10:26:29 +0100 Subject: [ATM] astigmatism question References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL><974920.36609.qm@web54501.mail.re2.yahoo.com><73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> <005a01c99c77$47d5b940$8f78fea9@amd> Message-ID: <2A8743AE2D0649EEB22403A744BDA47F@piv555a133b59e> >Testing a spherical mirror for astigmatism is best done in my >opinion by bringing the grating near the ROC and getting it to >where there is one band spreading across almost half the mirror's >width. Astig will show up as an S shaped line rather than a >stright one. At the level ATM metrology is now, the best way to test for astigmatism in qualitative and fully quantitative way is interferometry. In particular Bath interferometry. results are incomparably better, but time saved is worth of consideration as well. You can forget guesswork. The involved equipment is simple and comparable to Foucault tester in complexity, data reduction software is available for free, its use is tutored by experienced people not to mention that authors are very helpful. Effort in making Bath interferometer is negligible compared to what you have to invest in mirror making. Regards Vladimir. From dlwebb at canit.se Wed Mar 4 18:53:54 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Wed, 4 Mar 2009 10:53:54 +0100 (MET) Subject: [ATM] Eyepiece question In-Reply-To: <000801c999fb$19eeef20$8f78fea9@amd> Message-ID: On Sat, 28 Feb 2009, Bob May wrote: > I'd not consider buying any zoom type EP as they are all a severe > comprimise as far as optics goes. Generally narrow filds of view > and soft focus are the biggest problems right off the bat. If > you want it as a toy, go ahead and buy it but it really isn't > worth the prices for them. > Bob May The only such eyepiece I have like this is more or less permanently attached to refractor scope. There is a lot of what I think is called lateral color. That is, red vs blue colored images are slightly separated, so image of something like a branch appears wider than it should be. One side looks too red, the other side too blue and in between something closer to "correct" color. This only worsens with zoom. My other eyepieces on other scopes do not do this, at least not so exteme. Stopping the objective down (from 86 mm to 15 mm diameter) seems to have helped. I wonder if this is common feature of this type of eyepiece? Dominic From jroyston at gmx.de Wed Mar 4 19:41:49 2009 From: jroyston at gmx.de (Jeremy Royston) Date: Wed, 4 Mar 2009 11:41:49 +0100 Subject: [ATM] astigmatism question In-Reply-To: <2A8743AE2D0649EEB22403A744BDA47F@piv555a133b59e> References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL><974920.36609.qm@web54501.mail.re2.yahoo.com><73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> <005a01c99c77$47d5b940$8f78fea9@amd> <2A8743AE2D0649EEB22403A744BDA47F@piv555a133b59e> Message-ID: <002001c99cb5$d32523d0$796f6b70$@de> Hello all, as a simple test, use a point light source and look at the image with a short focus eyepiece (5mm). You can see examples with the Aberrator http://aberrator.astronomy.net/ and Diffract programs http://home.earthlink.net/~burrjaw/atm/odyframe.htm As previously noted, the Foucault and Ronchi tests are unsuitable for detecting and measuring astigmatism, they won't see it unless it is extreme The 2D Hartmann test (also http://home.earthlink.net/~burrjaw/atm/odyframe.htm ) is a simpler alternative to the Bath test, I'm sold on it Best wishes, Jerry -----Urspr?ngliche Nachricht----- Von: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] Im Auftrag von Vladimir Galogaza Gesendet: Mittwoch, 4. M?rz 2009 10:26 An: ATM List Betreff: Re: [ATM] astigmatism question >Testing a spherical mirror for astigmatism is best done in my >opinion by bringing the grating near the ROC and getting it to >where there is one band spreading across almost half the mirror's >width. Astig will show up as an S shaped line rather than a >stright one. From neil at astronomy.ndo.co.uk Wed Mar 4 19:38:01 2009 From: neil at astronomy.ndo.co.uk (Neil Booker) Date: Wed, 4 Mar 2009 10:38:01 -0000 Subject: [ATM] I am about to drill a hole in my aluminum tube References: <825309.84511.qm@web110109.mail.gq1.yahoo.com> Message-ID: <00e901c99cb7$7b36b1a0$99fafea9@laura> Hi John I wrote:- > P.S. Using Richard Berry's Build your own telescope (page 27), I make it 79 11/16. You replied:- >Neil, >I think you're answer is correct. >John Thanks, but it's Richard Berry who's right. I just put Francis' numbers in the right place and pressed the correct buttons on the calculator. Neil From foreilly at bestweb.net Wed Mar 4 22:05:12 2009 From: foreilly at bestweb.net (Francis J. O'Reilly) Date: Wed, 4 Mar 2009 08:05:12 -0500 Subject: [ATM] I am about to drill a hole in my aluminum tube References: <825309.84511.qm@web110109.mail.gq1.yahoo.com> <00e901c99cb7$7b36b1a0$99fafea9@laura> Message-ID: <35235C9654BA40A19C21B5840F5D6438@D5GHLR11> Neil and Richard, Thank you for your help. I am now taking steps to remeasure everything carefully and exactly. Francis ----- Original Message ----- From: "Neil Booker" To: "AMT LIST" Sent: Wednesday, March 04, 2009 5:38 AM Subject: Re: [ATM] I am about to drill a hole in my aluminum tube > Hi John > > I wrote:- >> P.S. Using Richard Berry's Build your own telescope (page 27), I make it > 79 > 11/16. > > You replied:- >>Neil, >>I think you're answer is correct. >>John > > Thanks, but it's Richard Berry who's right. I just put Francis' numbers in > the right place and pressed the correct buttons on the calculator. > > Neil > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From jhissong at gmail.com Wed Mar 4 22:59:54 2009 From: jhissong at gmail.com (Jason Hissong) Date: Wed, 4 Mar 2009 08:59:54 -0500 Subject: [ATM] 8 inch f/5 too fast? In-Reply-To: <003101c99c72$788d49e0$8f78fea9@amd> References: <49ABFCE8.5010901@gmail.com> <003101c99c72$788d49e0$8f78fea9@amd> Message-ID: My first two mirrors (an 8" and a 12.5") were around F4.2. I did manage to get them both to be about 1/7th wave and they provide satisfactory views. My 6" F/6 should be a cake walk.. heheheheh. Jason On Tue, Mar 3, 2009 at 9:39 PM, Bob May wrote: > A F5 will do fine, especially as a first telescope for all of the > larger things in the sky. ?You won't be doing too well with it as > a planetary scope tho as you won't be getting that much > magnification. ?It does give you a definite choice for a second > scope, one being of at least F10 which will be a lot better for > doing planetary work. > Bob May > > rmay at nethere.com > http: slash /nav.to slash bobmay > http: slash /bobmay dot astronomy.net > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From jack.swaton at starryhost.com Thu Mar 5 00:10:18 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Wed, 4 Mar 2009 07:10:18 -0800 Subject: [ATM] Star Images and Optical Components Message-ID: <66F0D019AC8243AA80BF4E320343D207@MRBNOTEBOOK> What I'm trying to do is understand the difference between star images due to mirror quality, secondary quality, secondary size, secondary support structure (wire versus curved versus straight vaned), primary flexure (or in-flexure due to massive amounts of silicone), etc.. So what do star images look like at different wave fronts? Are they less round? More fuzzy? What are the practical things to look for when viewing through my Coulter mirrors versus a Pegasus mirror or outstanding mirror you gentlefolks make so well? What I'm trying to do is understand the difference between star images due to mirror quality, secondary quality, secondary size, secondary support structure (wire versus curved versus straight vaned), etc. Jack Swaton www.StarryHost.com From s.c.koehler at gmail.com Thu Mar 5 00:45:06 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Wed, 4 Mar 2009 09:45:06 -0600 Subject: [ATM] Star Images and Optical Components In-Reply-To: <66F0D019AC8243AA80BF4E320343D207@MRBNOTEBOOK> References: <66F0D019AC8243AA80BF4E320343D207@MRBNOTEBOOK> Message-ID: <8d3a545d0903040745y21e592dft997298c9ee9aea35@mail.gmail.com> Jack, > What I'm trying to do is understand the difference between star images due > to mirror quality, secondary quality, secondary size, secondary support > structure (wire versus curved versus straight vaned), primary flexure (or > in-flexure due to massive amounts of silicone), etc.. Two invaluable resources for understanding these things are: Star Testing Astronomical Telescopes by Harold Suiter and the free program Aberrator by Cor Berrevoets -- Steve Koehler From al at sgi.com Thu Mar 5 02:46:20 2009 From: al at sgi.com (Alexis Cousein) Date: Wed, 04 Mar 2009 18:46:20 +0100 Subject: [ATM] Overlooked value of an RFT / Short F Ratio Newt In-Reply-To: <529F9DA5-7958-428D-AD13-E8901329DF0A@ct-astronomer.com> References: <529F9DA5-7958-428D-AD13-E8901329DF0A@ct-astronomer.com> Message-ID: <49AEBE6C.4040503@sgi.com> Shane LaPierre wrote: > Since the primary optical issue of a short focal ratio Newtonian is > coma, the best way to avoid coma is to use high power. This ensures > that the image under focus is close to the optical axis, If the scope is perfectly collimated. > minimizing > coma. It minimizes the linear size of coma in the focal plane, but the *angular* size of coma in an eyepiece X degrees off-axis in the apparent field of view remains the same - increase the power and you're using a portion of the field with less coma, but you magnify it more, and these effects cancel out. Coma only starts to be less intrusive if you make the eyepiece AFOV smaller, or magnify so much that the main diffraction pattern (the Airy diffraction pattern caused by the aperture) starts to blur the comatic tails. > This is opposite the traditional thought that a smallish short > focal ratio Newtonian is best used for wide-field viewing only. There are other reasons for disliking them for planetary work. Depth of focus is small and focusing is more difficult, and under f/4.5 most simple eyepiece designs will start to generate on-axis spherical aberration (though this is something you can fix with a really good barlow, or a complex eyepiece design like a Radian that tolerates fast scopes well, which is essentially using the same trick). And that's on a correctly collimated scope... From bthomas32000 at yahoo.com Thu Mar 5 06:01:42 2009 From: bthomas32000 at yahoo.com (Bill Thomas) Date: Wed, 4 Mar 2009 13:01:42 -0800 (PST) Subject: [ATM] astigmatism question Message-ID: <381308.25919.qm@web31006.mail.mud.yahoo.com> might want to try Jean Texereau's method p80-82 http://www.willbell.com/tm/tm3.htm. trick is to replace the slitless KE source with the ball bearing such that the reflection off the ball and then off the mirror returns to where the KE eye was. and if you find you have a some astigmatism use the method described in "A Manual for Amateur Telescope Makers" Lecleire p 231-238 http://www.willbell.com/tm/atmmanual/index.htm to correct the problem. Ted Cohen wrote: >I'm working to get spherical and I've detected some minor astigmatism that I >believe is actually in the mirror and not in my test setup. My question is: >if henceforth I use the correct technique such that no additional astigmatic >aberration is applied to the glass, will the existing astigmatism tend to >clear up over time? Or, does this type of aberration become amplified if not >cured early on in polishing? The question is to help me decide how >aggressively I need to address the problem. I think I have the understanding >necessary to interpret and apply the proper correction, but would prefer (if >feasible) to address this with further polishing action and a proper >technique, without resorting to asymmetrical stroking/pressure. From rmay at nethere.com Thu Mar 5 06:24:21 2009 From: rmay at nethere.com (Bob May) Date: Wed, 4 Mar 2009 13:24:21 -0800 Subject: [ATM] Eyepiece question References: Message-ID: <001a01c99d0f$963696c0$8f78fea9@amd> I'd suspect that your EP has some assembly or construction errors in it. What I've usually seen is SA and distortion for the most part followed by a relatively narrow FOV for its size. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Thu Mar 5 06:27:31 2009 From: rmay at nethere.com (Bob May) Date: Wed, 4 Mar 2009 13:27:31 -0800 Subject: [ATM] Star Images and Optical Components References: <66F0D019AC8243AA80BF4E320343D207@MRBNOTEBOOK> Message-ID: <002701c99d10$0794ce40$8f78fea9@amd> Some of the things mentioned are causes of wavefront errors while others are image defects. The shape of the mirrors will cause wavefront errors while things like secondary size and spiders will only affect the image itself. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From s.c.koehler at gmail.com Thu Mar 5 06:47:10 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Wed, 4 Mar 2009 15:47:10 -0600 Subject: [ATM] Star Images and Optical Components In-Reply-To: <002701c99d10$0794ce40$8f78fea9@amd> References: <66F0D019AC8243AA80BF4E320343D207@MRBNOTEBOOK> <002701c99d10$0794ce40$8f78fea9@amd> Message-ID: <8d3a545d0903041347i54915ae8ne541c4a137433429@mail.gmail.com> Bob, > Some of the things mentioned are causes of wavefront errors while > others are image defects. ?The shape of the mirrors will cause > wavefront errors while things like secondary size and spiders > will only affect the image itself. I disagree. The shape of the pupil (i.e., secondary, spiders, etc.) shows up in the wavefront, too. The incoming wavefront contains both amplitude and phase. Mirror aberrations affect the phase. Obstructions, etc, affect the amplitude. Both are part of the wavefront. Perhaps I misunderstood you. I didn't get the distinction between wavefront errors and image defects. -- Steve Koehler From jack.swaton at starryhost.com Thu Mar 5 08:39:48 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Wed, 4 Mar 2009 15:39:48 -0800 Subject: [ATM] Star Images and Optical Components In-Reply-To: <8d3a545d0903041347i54915ae8ne541c4a137433429@mail.gmail.com> References: <66F0D019AC8243AA80BF4E320343D207@MRBNOTEBOOK><002701c99d10$0794ce40$8f78fea9@amd> <8d3a545d0903041347i54915ae8ne541c4a137433429@mail.gmail.com> Message-ID: What is the difference between a 1/10th mirror and a 1/4 mirror? I'm assuming my Coulters are 1/4's. What is the difference at the eyepiece? Is it contrast? Or perhaps lack of sharpness? Jack -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Stephen Koehler Sent: Wednesday, March 04, 2009 1:47 PM To: Bob May Cc: atm at atmlist.net Subject: Re: [ATM] Star Images and Optical Components Bob, > Some of the things mentioned are causes of wavefront errors while > others are image defects. ?The shape of the mirrors will cause > wavefront errors while things like secondary size and spiders > will only affect the image itself. I disagree. The shape of the pupil (i.e., secondary, spiders, etc.) shows up in the wavefront, too. The incoming wavefront contains both amplitude and phase. Mirror aberrations affect the phase. Obstructions, etc, affect the amplitude. Both are part of the wavefront. Perhaps I misunderstood you. I didn't get the distinction between wavefront errors and image defects. -- Steve Koehler _______________________________________________ ATM mailing list http://www.atmlist.net/ From jack.swaton at starryhost.com Thu Mar 5 08:37:58 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Wed, 4 Mar 2009 15:37:58 -0800 Subject: [ATM] Star Images and Optical Components In-Reply-To: <8d3a545d0903040745y21e592dft997298c9ee9aea35@mail.gmail.com> References: <66F0D019AC8243AA80BF4E320343D207@MRBNOTEBOOK> <8d3a545d0903040745y21e592dft997298c9ee9aea35@mail.gmail.com> Message-ID: <00CB5BC2C65A4B839871BD38CD951277@MRBNOTEBOOK> Thanks, Steve. Per your suggestion, I'm looking at the software. I'll have to check the book out at the library. I'm having to learn how the software works, what the terms mean and how they apply to what I see. Here's one thing I see at the eyepiece: double offset images. For instance, Jupiter will have a twin shadowing itself just a tad. Jack -----Original Message----- From: Stephen Koehler [mailto:s.c.koehler at gmail.com] Sent: Wednesday, March 04, 2009 7:45 AM To: Jack Swaton @ Starry Host Cc: atm at atmlist.net Subject: Re: [ATM] Star Images and Optical Components Jack, > What I'm trying to do is understand the difference between star images due > to mirror quality, secondary quality, secondary size, secondary support > structure (wire versus curved versus straight vaned), primary flexure (or > in-flexure due to massive amounts of silicone), etc.. Two invaluable resources for understanding these things are: Star Testing Astronomical Telescopes by Harold Suiter and the free program Aberrator by Cor Berrevoets -- Steve Koehler From atmpob at yahoo.com Thu Mar 5 09:37:11 2009 From: atmpob at yahoo.com (Dale Eason) Date: Wed, 4 Mar 2009 16:37:11 -0800 (PST) Subject: [ATM] Star Images and Optical Components In-Reply-To: Message-ID: <291651.80506.qm@web54501.mail.re2.yahoo.com> It is both. Where it really starts to show up is when you try to use higher magnifications by using shorter FL eyepieces. You reach a point with a poor mirror were everything is very blurry and you can't make out any more detail. It is like you can not find the right focus position. There is none all are just about as blurry. This happens at higher power for better mirrors and at lower power for poor mirrors. You can use aberrator to simulate the difference. What I tell people is to use your telescope until you are unsatisfied with the view. Then start diagnosing what is wrong. Many first time scope users usually are very happy with a poor mirror since they can still show them views that astound them. Dale Eason --- On Wed, 3/4/09, Jack Swaton @ Starry Host wrote: > From: Jack Swaton @ Starry Host > Subject: Re: [ATM] Star Images and Optical Components > To: "'Stephen Koehler'" , "'Bob May'" > Cc: atm at atmlist.net > Date: Wednesday, March 4, 2009, 5:39 PM > What is the difference between a 1/10th mirror and a 1/4 > mirror? I'm > assuming my Coulters are 1/4's. What is the difference > at the eyepiece? Is > it contrast? Or perhaps lack of sharpness? > > Jack > > -----Original Message----- > From: atm-bounces at atmlist.net > [mailto:atm-bounces at atmlist.net] On Behalf Of > Stephen Koehler > Sent: Wednesday, March 04, 2009 1:47 PM > To: Bob May > Cc: atm at atmlist.net > Subject: Re: [ATM] Star Images and Optical Components > > Bob, > > > Some of the things mentioned are causes of wavefront > errors while > > others are image defects. ?The shape of the mirrors > will cause > > wavefront errors while things like secondary size and > spiders > > will only affect the image itself. > > I disagree. The shape of the pupil (i.e., secondary, > spiders, etc.) > shows up in the wavefront, too. The incoming wavefront > contains both > amplitude and phase. Mirror aberrations affect the phase. > Obstructions, etc, affect the amplitude. Both are part of > the > wavefront. > > Perhaps I misunderstood you. I didn't get the > distinction between > wavefront errors and image defects. > > -- > Steve Koehler > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From jack.swaton at starryhost.com Thu Mar 5 11:11:58 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Wed, 4 Mar 2009 18:11:58 -0800 Subject: [ATM] Star Images and Optical Components In-Reply-To: <291651.80506.qm@web54501.mail.re2.yahoo.com> References: <291651.80506.qm@web54501.mail.re2.yahoo.com> Message-ID: Dale, That's a very useful and practical description. Thanks. Does anybody know why I get double images on things, especially planets? For instance, Jupiter has a twin shadowing it by let's say 1/8 of it's globe. Is that an misplaced secondary? Jack -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Dale Eason Sent: Wednesday, March 04, 2009 4:37 PM To: atm at atmlist.net Subject: Re: [ATM] Star Images and Optical Components It is both. Where it really starts to show up is when you try to use higher magnifications by using shorter FL eyepieces. You reach a point with a poor mirror were everything is very blurry and you can't make out any more detail. It is like you can not find the right focus position. There is none all are just about as blurry. This happens at higher power for better mirrors and at lower power for poor mirrors. You can use aberrator to simulate the difference. What I tell people is to use your telescope until you are unsatisfied with the view. Then start diagnosing what is wrong. Many first time scope users usually are very happy with a poor mirror since they can still show them views that astound them. Dale Eason --- On Wed, 3/4/09, Jack Swaton @ Starry Host wrote: > From: Jack Swaton @ Starry Host > Subject: Re: [ATM] Star Images and Optical Components > To: "'Stephen Koehler'" , "'Bob May'" > Cc: atm at atmlist.net > Date: Wednesday, March 4, 2009, 5:39 PM > What is the difference between a 1/10th mirror and a 1/4 > mirror? I'm > assuming my Coulters are 1/4's. What is the difference > at the eyepiece? Is > it contrast? Or perhaps lack of sharpness? > > Jack > > -----Original Message----- > From: atm-bounces at atmlist.net > [mailto:atm-bounces at atmlist.net] On Behalf Of > Stephen Koehler > Sent: Wednesday, March 04, 2009 1:47 PM > To: Bob May > Cc: atm at atmlist.net > Subject: Re: [ATM] Star Images and Optical Components > > Bob, > > > Some of the things mentioned are causes of wavefront > errors while > > others are image defects. ?The shape of the mirrors > will cause > > wavefront errors while things like secondary size and > spiders > > will only affect the image itself. > > I disagree. The shape of the pupil (i.e., secondary, > spiders, etc.) > shows up in the wavefront, too. The incoming wavefront > contains both > amplitude and phase. Mirror aberrations affect the phase. > Obstructions, etc, affect the amplitude. Both are part of > the > wavefront. > > Perhaps I misunderstood you. I didn't get the > distinction between > wavefront errors and image defects. > > -- > Steve Koehler > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ From foreilly at verizon.net Thu Mar 5 11:17:04 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Wed, 04 Mar 2009 21:17:04 -0500 Subject: [ATM] Star Images and Optical Components References: <291651.80506.qm@web54501.mail.re2.yahoo.com> Message-ID: <57D18BEA48664B978A9CBFAA5C9E9E34@HELENYLCMWAV95> Jack, Some years ago the Westchester Amateur Astronomers in lower NY had a similar problem with an eight inch f/6 that we built after the club member transporting the telescope to it's first light party had a mishap in which the mirror came loose and rolled forward in the tube. It turned out that there was a small crack in the secondary mirror which created double images on one side of the tube. Alternately, if you have a plate glass secondary, it may not have equalized in temprature. Best, Francis J. O'Reilly ----- Original Message ----- From: "Jack Swaton @ Starry Host" To: ; Sent: Wednesday, March 04, 2009 9:11 PM Subject: Re: [ATM] Star Images and Optical Components Dale, That's a very useful and practical description. Thanks. Does anybody know why I get double images on things, especially planets? For instance, Jupiter has a twin shadowing it by let's say 1/8 of it's globe. Is that an misplaced secondary? Jack -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Dale Eason Sent: Wednesday, March 04, 2009 4:37 PM To: atm at atmlist.net Subject: Re: [ATM] Star Images and Optical Components It is both. Where it really starts to show up is when you try to use higher magnifications by using shorter FL eyepieces. You reach a point with a poor mirror were everything is very blurry and you can't make out any more detail. It is like you can not find the right focus position. There is none all are just about as blurry. This happens at higher power for better mirrors and at lower power for poor mirrors. You can use aberrator to simulate the difference. What I tell people is to use your telescope until you are unsatisfied with the view. Then start diagnosing what is wrong. Many first time scope users usually are very happy with a poor mirror since they can still show them views that astound them. Dale Eason --- On Wed, 3/4/09, Jack Swaton @ Starry Host wrote: > From: Jack Swaton @ Starry Host > Subject: Re: [ATM] Star Images and Optical Components > To: "'Stephen Koehler'" , "'Bob May'" > Cc: atm at atmlist.net > Date: Wednesday, March 4, 2009, 5:39 PM > What is the difference between a 1/10th mirror and a 1/4 > mirror? I'm > assuming my Coulters are 1/4's. What is the difference > at the eyepiece? Is > it contrast? Or perhaps lack of sharpness? > > Jack > > -----Original Message----- > From: atm-bounces at atmlist.net > [mailto:atm-bounces at atmlist.net] On Behalf Of > Stephen Koehler > Sent: Wednesday, March 04, 2009 1:47 PM > To: Bob May > Cc: atm at atmlist.net > Subject: Re: [ATM] Star Images and Optical Components > > Bob, > > > Some of the things mentioned are causes of wavefront > errors while > > others are image defects. The shape of the mirrors > will cause > > wavefront errors while things like secondary size and > spiders > > will only affect the image itself. > > I disagree. The shape of the pupil (i.e., secondary, > spiders, etc.) > shows up in the wavefront, too. The incoming wavefront > contains both > amplitude and phase. Mirror aberrations affect the phase. > Obstructions, etc, affect the amplitude. Both are part of > the > wavefront. > > Perhaps I misunderstood you. I didn't get the > distinction between > wavefront errors and image defects. > > -- > Steve Koehler > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ From s.c.koehler at gmail.com Thu Mar 5 11:51:42 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Wed, 4 Mar 2009 20:51:42 -0600 Subject: [ATM] Star Images and Optical Components In-Reply-To: References: <291651.80506.qm@web54501.mail.re2.yahoo.com> Message-ID: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com> Jack, > Does anybody know why I get double images on things, especially planets? For > instance, Jupiter has a twin shadowing it by let's say 1/8 of it's globe. Is > that an misplaced secondary? I think that is likely a problem with your eye. Does the double image rotate, if you rotate your head? I have some amount of astigmatism in both my eyes. I see any bright object (like the moon, naked eye) double. It's really a problem reading freeway signs at night, as each letter is offset diagonally. -- Steve Koehler From tcohen at blakeglobal.com Thu Mar 5 13:01:25 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Wed, 4 Mar 2009 20:01:25 -0800 Subject: [ATM] astigmatism question In-Reply-To: <381308.25919.qm@web31006.mail.mud.yahoo.com> References: <381308.25919.qm@web31006.mail.mud.yahoo.com> Message-ID: <577AFF371DAD476096F8EF9E907BD471@BLAKESF.LOCAL> All, I was able to take several crude Ronchigrams of my current state of affairs and have attached a link to one of these. The astigmatism is evident and confirmed by rotation in four orientations. Note astigmatism in the picture at 10 o'clock and 4 o'clock. Some of the astigmatism is apparently caused by slumping of the glass when in the horizontal position - but not all. Also, note the central depression is not in the center of the mirror. As I said before, I'm in the middle of polishing - most of the pits are out but I'm a considerable way from spherical. The picture shown represents a vast improvement over when I started polishing. There's a low zone at 85% to 95% and the marginal zone appears to be raised. It's definitely a work in progress as it looks more like a bowl of spaghetti than a optical mirror. I think the astigmatism was caused by an experimental stroke I was trying - there's no need for me to specify what I was doing - but I'm certainly not going to do it anymore. http://tinyurl.com/bolntm From dlwebb at canit.se Thu Mar 5 18:45:46 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Thu, 5 Mar 2009 10:45:46 +0100 (MET) Subject: [ATM] Star Images and Optical Components In-Reply-To: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com> Message-ID: On Wed, 4 Mar 2009, Stephen Koehler wrote: > Jack, > > > Does anybody know why I get double images on things, especially planets? For > > instance, Jupiter has a twin shadowing it by let's say 1/8 of it's globe. Is > > that an misplaced secondary? > > I think that is likely a problem with your eye. Does the double image > rotate, if you rotate your head? I have some amount of astigmatism in > both my eyes. I see any bright object (like the moon, naked eye) > double. It's really a problem reading freeway signs at night, as each > letter is offset diagonally. > > -- > Steve Koehler I am not so sure. Telescopes usually only have one eyepiece. While double vision can occur in one eye (called monocular diplopia), this is not terribly common. I am over 40 and happen to have it myself, but also seem to have normal vision otherwise. Diplopia happens with some medications, but would be expected to effect both eyes. Doctor thinks this is problem with eye muscles that need exercise and indeed some exercises help me. I think this makes viewing through different eyepeices, etc more comfortable. However, moving my head further away from what I need to focus on or using 2+ reading glasses completely eliminates this. I have a scope that can give double images, but comparable scopes that do not. I suspect most of these are truly in the optical system and not the eye. You can easily sort this out with a webcam with the lens removed. Dominic From jack.swaton at starryhost.com Thu Mar 5 23:05:43 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Thu, 5 Mar 2009 06:05:43 -0800 Subject: [ATM] Star Images and Optical Components In-Reply-To: References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com> Message-ID: <0F1EAC818AD8499A85E44393CE11BE91@MRBNOTEBOOK> Interesting observations. I know I do have some astigmatism which I can tell by "rotating my head" and the image shifts, but this is more severe and I'll have to see if it happens on say, Jupiter. I still suspect poor craftsmanship (mine) on my optical train. You suggest a web cam...how do I use that to diagnose this? I have an old web cam from the early days that was used for Internet chats and that's it. And I'm too poor at the moment to acquire anything that costs more than 25 cents. By the way, I LOVE your "ATM Superheros" moniker for the group. Very thoughtful. Jack -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Dominic-Luc Webb Sent: Thursday, March 05, 2009 1:46 AM To: ATM Superheros Subject: Re: [ATM] Star Images and Optical Components On Wed, 4 Mar 2009, Stephen Koehler wrote: > Jack, > > > Does anybody know why I get double images on things, especially planets? For > > instance, Jupiter has a twin shadowing it by let's say 1/8 of it's globe. Is > > that an misplaced secondary? > > I think that is likely a problem with your eye. Does the double image > rotate, if you rotate your head? I have some amount of astigmatism in > both my eyes. I see any bright object (like the moon, naked eye) > double. It's really a problem reading freeway signs at night, as each > letter is offset diagonally. > > -- > Steve Koehler I am not so sure. Telescopes usually only have one eyepiece. While double vision can occur in one eye (called monocular diplopia), this is not terribly common. I am over 40 and happen to have it myself, but also seem to have normal vision otherwise. Diplopia happens with some medications, but would be expected to effect both eyes. Doctor thinks this is problem with eye muscles that need exercise and indeed some exercises help me. I think this makes viewing through different eyepeices, etc more comfortable. However, moving my head further away from what I need to focus on or using 2+ reading glasses completely eliminates this. I have a scope that can give double images, but comparable scopes that do not. I suspect most of these are truly in the optical system and not the eye. You can easily sort this out with a webcam with the lens removed. Dominic _______________________________________________ ATM mailing list http://www.atmlist.net/ From dlwebb at canit.se Thu Mar 5 23:40:02 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Thu, 5 Mar 2009 15:40:02 +0100 (MET) Subject: [ATM] Star Images and Optical Components In-Reply-To: <0F1EAC818AD8499A85E44393CE11BE91@MRBNOTEBOOK> Message-ID: On Thu, 5 Mar 2009, Jack Swaton @ Starry Host wrote: > I still suspect poor craftsmanship (mine) on my optical train. > You suggest a web cam...how do I use that to diagnose this? I have an old > web cam from the early days that was used for Internet chats and that's it. > And I'm too poor at the moment to acquire anything that costs more than 25 > cents. Money is non-issue. You should be able to focus your webcam without removing the lens by focusing to infinity. I simply prefer removing it. These lenses are usually easy to remove. > By the way, I LOVE your "ATM Superheros" moniker for the group. Very > thoughtful. > > Jack This is an important breed of superhero, not to be trivialized by discussing in the same breathe as those other Hollywood types. Dominic From s.c.koehler at gmail.com Fri Mar 6 00:09:04 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Thu, 5 Mar 2009 09:09:04 -0600 Subject: [ATM] Star Images and Optical Components In-Reply-To: References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com> Message-ID: <8d3a545d0903050709v5eb1d01i44ab62d6cc009d75@mail.gmail.com> Dominic, > I am not so sure. Telescopes usually only have one eyepiece. While > double vision can occur in one eye (called monocular diplopia), > this is not terribly common. I don't know how common it is, but I definitely have this. It is only noticeable at night on high-contrast, bright objects when my eyes are dilated. -- Steve Koehler From mjc5 at psu.edu Fri Mar 6 00:53:52 2009 From: mjc5 at psu.edu (Michael Coslo) Date: Thu, 05 Mar 2009 10:53:52 -0500 Subject: [ATM] Star Images and Optical Components In-Reply-To: <8d3a545d0903050709v5eb1d01i44ab62d6cc009d75@mail.gmail.com> References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com> <8d3a545d0903050709v5eb1d01i44ab62d6cc009d75@mail.gmail.com> Message-ID: <237C6AA1-925B-4954-A902-548F2F0FC2C3@psu.edu> On Mar 5, 2009, at 10:09 AM, Stephen Koehler wrote: > Dominic, > >> I am not so sure. Telescopes usually only have one eyepiece. While >> double vision can occur in one eye (called monocular diplopia), >> this is not terribly common. > > I don't know how common it is, but I definitely have this. It is only > noticeable at night on high-contrast, bright objects when my eyes are > dilated. Have you by any chance had Lasik surgery? -73 de Mike N3LI - From s.c.koehler at gmail.com Fri Mar 6 01:12:29 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Thu, 5 Mar 2009 10:12:29 -0600 Subject: [ATM] Star Images and Optical Components In-Reply-To: <237C6AA1-925B-4954-A902-548F2F0FC2C3@psu.edu> References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com> <8d3a545d0903050709v5eb1d01i44ab62d6cc009d75@mail.gmail.com> <237C6AA1-925B-4954-A902-548F2F0FC2C3@psu.edu> Message-ID: <8d3a545d0903050812p47fa14e4sd36fa85c3e2695ed@mail.gmail.com> Mike, >> I don't know how common it is, but I definitely have this. ?It is only >> noticeable at night on high-contrast, bright objects when my eyes are >> dilated. > > > Have you by any chance had Lasik surgery? No, I haven't. In general, my eyes are pretty good--I have never had to wear corrective lenses. Since about the age of 45, I have had to use reading glasses more and more, but that's a different problem. Since I don't wear glasses, I have not seen an eye specialist all that often. However, the astigmatism was diagnosed when I was about 20. -- Steve Koehler From tcohen at blakeglobal.com Fri Mar 6 02:44:27 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Thu, 5 Mar 2009 09:44:27 -0800 Subject: [ATM] astigmatism correction In-Reply-To: <577AFF371DAD476096F8EF9E907BD471@BLAKESF.LOCAL> References: <381308.25919.qm@web31006.mail.mud.yahoo.com> <577AFF371DAD476096F8EF9E907BD471@BLAKESF.LOCAL> Message-ID: <6F4CC628F40246F0AB6836CB24DD7679@BLAKESF.LOCAL> I feel much better after viewing the affect of two wets with a normal stroke (center over the 50% zone / 4-inch overhang) - everything is much improved. Will post an updated Ronchigram in a few weeks. Thanks for all your suggestions. I got scared by the astig., but it's not that bad, and seems to correct itself when using the proper technique. -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Ted Cohen Sent: Wednesday, March 04, 2009 8:01 PM To: atm at atmlist.net Subject: Re: [ATM] astigmatism question All, I was able to take several crude Ronchigrams of my current state of affairs and have attached a link to one of these. The astigmatism is evident and confirmed by rotation in four orientations. Note astigmatism in the picture at 10 o'clock and 4 o'clock. Some of the astigmatism is apparently caused by slumping of the glass when in the horizontal position - but not all. Also, note the central depression is not in the center of the mirror. As I said before, I'm in the middle of polishing - most of the pits are out but I'm a considerable way from spherical. The picture shown represents a vast improvement over when I started polishing. There's a low zone at 85% to 95% and the marginal zone appears to be raised. It's definitely a work in progress as it looks more like a bowl of spaghetti than a optical mirror. I think the astigmatism was caused by an experimental stroke I was trying - there's no need for me to specify what I was doing - but I'm certainly not going to do it anymore. http://tinyurl.com/bolntm _______________________________________________ ATM mailing list http://www.atmlist.net/ From jack.swaton at starryhost.com Fri Mar 6 03:43:54 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Thu, 5 Mar 2009 10:43:54 -0800 Subject: [ATM] Star Images and Optical Components In-Reply-To: <8d3a545d0903050812p47fa14e4sd36fa85c3e2695ed@mail.gmail.com> References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com><8d3a545d0903050709v5eb1d01i44ab62d6cc009d75@mail.gmail.com><237C6AA1-925B-4954-A902-548F2F0FC2C3@psu.edu> <8d3a545d0903050812p47fa14e4sd36fa85c3e2695ed@mail.gmail.com> Message-ID: <4B130BF73E2A4272AFCE96FAB475636E@MRBNOTEBOOK> Same here: no lasik and mild reading prescription glasses. The optho did not mention (probably did not look for) the double image problem. Interesting description of the double circumstances: "only noticeable at night on high-contrast, bright objects". I will have to do some testing. Jack -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Stephen Koehler Sent: Thursday, March 05, 2009 8:12 AM To: Michael Coslo Cc: ATM Superheros Subject: Re: [ATM] Star Images and Optical Components Mike, >> I don't know how common it is, but I definitely have this. ?It is only >> noticeable at night on high-contrast, bright objects when my eyes are >> dilated. > > > Have you by any chance had Lasik surgery? No, I haven't. In general, my eyes are pretty good--I have never had to wear corrective lenses. Since about the age of 45, I have had to use reading glasses more and more, but that's a different problem. Since I don't wear glasses, I have not seen an eye specialist all that often. However, the astigmatism was diagnosed when I was about 20. -- Steve Koehler _______________________________________________ ATM mailing list http://www.atmlist.net/ From jack.swaton at starryhost.com Fri Mar 6 03:46:41 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Thu, 5 Mar 2009 10:46:41 -0800 Subject: [ATM] Star Images and Optical Components In-Reply-To: References: <0F1EAC818AD8499A85E44393CE11BE91@MRBNOTEBOOK> Message-ID: <63B90775AEAD45C0AC7CA1BB2BD86ED7@MRBNOTEBOOK> Dominic, OK, so I can try and dig out the old webcam and do (or not) remove the lens, but then what? What am I trying to do? Take a picture to post for others to diagnose? What? Thanks, Jack -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Dominic-Luc Webb Sent: Thursday, March 05, 2009 6:40 AM To: ATM Superheros Subject: Re: [ATM] Star Images and Optical Components On Thu, 5 Mar 2009, Jack Swaton @ Starry Host wrote: > I still suspect poor craftsmanship (mine) on my optical train. > You suggest a web cam...how do I use that to diagnose this? I have an old > web cam from the early days that was used for Internet chats and that's it. > And I'm too poor at the moment to acquire anything that costs more than 25 > cents. Money is non-issue. You should be able to focus your webcam without removing the lens by focusing to infinity. I simply prefer removing it. These lenses are usually easy to remove. > By the way, I LOVE your "ATM Superheros" moniker for the group. Very > thoughtful. > > Jack This is an important breed of superhero, not to be trivialized by discussing in the same breathe as those other Hollywood types. Dominic _______________________________________________ ATM mailing list http://www.atmlist.net/ From shane at ct-astronomer.com Fri Mar 6 04:42:50 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Thu, 5 Mar 2009 14:42:50 -0500 Subject: [ATM] Overlooked value of an RFT / Short F Ratio Newt In-Reply-To: <49AEBE6C.4040503@sgi.com> References: <529F9DA5-7958-428D-AD13-E8901329DF0A@ct-astronomer.com> <49AEBE6C.4040503@sgi.com> Message-ID: <6A762CB9-2E15-4DB2-9354-6E8F56B7A2D3@ct-astronomer.com> On Mar 4, 2009, at 12:46 PM, Alexis Cousein wrote: > >> minimizing coma. > > It minimizes the linear size of coma in the focal plane, but the > *angular* > size of coma in an eyepiece X degrees off-axis in the apparent field > of > view remains the same - increase the power and you're using a portion > of the field with less coma, but you magnify it more, and these > effects > cancel out. > > Coma only starts to be less intrusive if you make the eyepiece AFOV > smaller, or magnify so much that the main diffraction pattern (the > Airy > diffraction pattern caused by the aperture) starts to blur the comatic > tails. This is the one I'd like to research the numbers on... Assuming a typical off-axis image plane at 200X magnification (I'll find stats on an eyepiece I have), I'd like to determine if coma is significant at the edge. I suspect it can't be that bad @ f4.2 with magnifications that high... then again I haven't run any numbers. I do get your point that although the off-axis coma is less the more 'on-axis' you are viewing, however it is also more magnified in a high-power eyepiece. I don't think having a small apparent FOV eyepiece is the solution :) Now the issue about depth of field is an obvious one. Take care, Shane LaPierre From rmay at nethere.com Fri Mar 6 06:33:03 2009 From: rmay at nethere.com (Bob May) Date: Thu, 5 Mar 2009 13:33:03 -0800 Subject: [ATM] Star Images and Optical Components References: <66F0D019AC8243AA80BF4E320343D207@MRBNOTEBOOK> <002701c99d10$0794ce40$8f78fea9@amd> <8d3a545d0903041347i54915ae8ne541c4a137433429@mail.gmail.com> Message-ID: <000e01c99dd9$f94e6ba0$8f78fea9@amd> All of the things mentioned are errors in the image. Things like a poorly shaped mirror does one thing to a mirror, things like putting the light in the wrong places. Other things like the pupil and spider effects are different as these are things that are not related to the shape of the optical surfaces but rather the requirements of the scope. You can get rid of spider diffreaction by putting a glass support for the secondary or doing an offset telescope. Things like the pupil are basic physical results of the design as there is nothing you can do about them. Things that happen with the shape of the mirrors or lenses from construction errors (like a 1/2 wave accurate primary) produce one type of errror while diffraction errors are from the mechanical construction decisions. Altogether different errors. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Fri Mar 6 06:41:44 2009 From: rmay at nethere.com (Bob May) Date: Thu, 5 Mar 2009 13:41:44 -0800 Subject: [ATM] Star Images and Optical Components References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com> <0F1EAC818AD8499A85E44393CE11BE91@MRBNOTEBOOK> Message-ID: <001d01c99ddb$53620060$8f78fea9@amd> The use of a camera with a removable lens of any kind/size is easy. The first way is through prime focus photography. Just take the lens off and watch the image on the TV or computer screen while you focus the image. With TV cameras, the moon or the bright planets are all you will be able to see as the exposure time just isn't that good for anything fainter. Larger scopes do make it easier to see the fainter stuff. Aperture does rule here! The second way is to focus the scope with an EP and then take the camera with its lens on and focus it to infinity and let it look at the EP output at close range. Autofocusing cameras do run into a problem here as they will try to focus to the surface of the EP which is also in view and completely miss the subject that the scope is looking at. Agin, only the really bright stuff can be seen with a TV camera. Webcams often can be run at slower speeds and usually allow for longer exposures as a result and be able to see fainter objects. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From jack.swaton at starryhost.com Fri Mar 6 06:46:44 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Thu, 5 Mar 2009 13:46:44 -0800 Subject: [ATM] Star Images and Optical Components In-Reply-To: <001d01c99ddb$53620060$8f78fea9@amd> References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com><0F1EAC818AD8499A85E44393CE11BE91@MRBNOTEBOOK> <001d01c99ddb$53620060$8f78fea9@amd> Message-ID: <0605BC2293114FCF861259DE42BAD7F3@MRBNOTEBOOK> Very good on the use of the camera, but the original suggestion (I thought) was to use the camera as a diagnostic tool for various elements of the optical train. If so, then how I am using it to that end? I may have TOTALLY missed the point of the use of the camera. Eagerly, Jack -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Bob May Sent: Thursday, March 05, 2009 1:42 PM To: atm at atmlist.net Subject: Re: [ATM] Star Images and Optical Components The use of a camera with a removable lens of any kind/size is easy. The first way is through prime focus photography. Just take the lens off and watch the image on the TV or computer screen while you focus the image. With TV cameras, the moon or the bright planets are all you will be able to see as the exposure time just isn't that good for anything fainter. Larger scopes do make it easier to see the fainter stuff. Aperture does rule here! The second way is to focus the scope with an EP and then take the camera with its lens on and focus it to infinity and let it look at the EP output at close range. Autofocusing cameras do run into a problem here as they will try to focus to the surface of the EP which is also in view and completely miss the subject that the scope is looking at. Agin, only the really bright stuff can be seen with a TV camera. Webcams often can be run at slower speeds and usually allow for longer exposures as a result and be able to see fainter objects. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net _______________________________________________ ATM mailing list http://www.atmlist.net/ From rmay at nethere.com Fri Mar 6 06:53:34 2009 From: rmay at nethere.com (Bob May) Date: Thu, 5 Mar 2009 13:53:34 -0800 Subject: [ATM] Overlooked value of an RFT / Short F Ratio Newt References: <529F9DA5-7958-428D-AD13-E8901329DF0A@ct-astronomer.com><49AEBE6C.4040503@sgi.com> <6A762CB9-2E15-4DB2-9354-6E8F56B7A2D3@ct-astronomer.com> Message-ID: <003601c99ddc$e008aa40$8f78fea9@amd> With EPs of any particular AFOV, the coma at the edge of the field should be the same, I think. That means that really the magnification of the EP is irrelevant but the AFOV is. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Fri Mar 6 07:08:04 2009 From: rmay at nethere.com (Bob May) Date: Thu, 5 Mar 2009 14:08:04 -0800 Subject: [ATM] Ronchi grating stripes References: <213922.95189.qm@web45104.mail.sp1.yahoo.com> Message-ID: <004901c99dde$dc6cfb00$8f78fea9@amd> Yep, I realize that .ps is a postscript file is all text. It, however is rather cmplex in how it defines a document. Since I didn't know where the name was, it is usually better to just fond out from where it was. Go down into the actual dext area and you will see what I mean. Basically, I have found that Postscript files can be read but are usually quite difficult with all of the instructions included in the file for spacing, etc. of the text. Thanks tho for seeing it. I really don't have any idea of why it would be in there tho as I don't know the other names in there. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From daze39 at earthlink.net Fri Mar 6 07:44:18 2009 From: daze39 at earthlink.net (David Weinshenker) Date: Thu, 05 Mar 2009 14:44:18 -0800 Subject: [ATM] Star Images and Optical Components In-Reply-To: <0605BC2293114FCF861259DE42BAD7F3@MRBNOTEBOOK> References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com><0F1EAC818AD8499A85E44393CE11BE91@MRBNOTEBOOK> <001d01c99ddb$53620060$8f78fea9@amd> <0605BC2293114FCF861259DE42BAD7F3@MRBNOTEBOOK> Message-ID: <49B055C2.1040601@earthlink.net> Jack Swaton @ Starry Host wrote: > Very good on the use of the camera, but the original suggestion (I thought) > was to use the camera as a diagnostic tool for various elements of the > optical train. If so, then how I am using it to that end? > > I may have TOTALLY missed the point of the use of the camera. Same general notes apply - for analysis, as well as imaging, it's a matter of setting things up so that the scope focuses its image onto the camera sensor (as Bob described). One thing you can do for analysis is to make a series of "focus run" images of a point source - find the focus setting at which the image is most nearly in focus, and then make a series of images at settings spanning that range: defocus in one direction until the image expands into a "donut" shape (with the secondary shadow clearly visible), and scan through best focus to a similar deviation from focus in the opposite direction, making images at various focus settings as you go. -dave w > > Eagerly, > Jack > > -----Original Message----- > From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of > Bob May > Sent: Thursday, March 05, 2009 1:42 PM > To: atm at atmlist.net > Subject: Re: [ATM] Star Images and Optical Components > > The use of a camera with a removable lens of any kind/size is > easy. > The first way is through prime focus photography. Just take the > lens off and watch the image on the TV or computer screen while > you focus the image. With TV cameras, the moon or the bright > planets are all you will be able to see as the exposure time just > isn't that good for anything fainter. Larger scopes do make it > easier to see the fainter stuff. Aperture does rule here! > The second way is to focus the scope with an EP and then take the > camera with its lens on and focus it to infinity and let it look > at the EP output at close range. Autofocusing cameras do run > into a problem here as they will try to focus to the surface of > the EP which is also in view and completely miss the subject that > the scope is looking at. Agin, only the really bright stuff can > be seen with a TV camera. > Webcams often can be run at slower speeds and usually allow for > longer exposures as a result and be able to see fainter objects. > Bob May > > rmay at nethere.com > http: slash /nav.to slash bobmay > http: slash /bobmay dot astronomy.net > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From rflrs at rcn.com Fri Mar 6 12:27:24 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Thu, 05 Mar 2009 22:27:24 -0500 Subject: [ATM] Another Reuse Message-ID: <49B0981C.7010305@rcn.com> There always seems to be a desire to be able to make one telescope and, later, enhance it with some upgrade. This is another example of that reuse. A 152.4 mm f/12.8 [green] aplanatic doublet: http://users.rcn.com/rflrs/Ptz11-63b.atm ATMOS input file http://users.rcn.com/rflrs/Ptz11-63b.len OSLO input file http://users.rcn.com/rflrs/Ptz11-63b.txt TEXT prescription http://users.rcn.com/rflrs/Ptz11-63b.zmx ZEMAX input file Modifying the spacing and adding a secondary doublet, one gets a 152.4 mm f/9.65 [green] anastigmatic Petzval: http://users.rcn.com/rflrs/Ptz11-63x.atm ATMOS input file http://users.rcn.com/rflrs/Ptz11-63x.len OSLO input file http://users.rcn.com/rflrs/Ptz11-63x.txt TEXT prescription http://users.rcn.com/rflrs/Ptz11-63x.zmx ZEMAX input file The unique feature here is that the modification actually reduces the air-space of the primary doublet to zero. The bonus here is that there is very little change in the F-C longitudinal crossover zone -- from less than 85% for the doublet to greater than 82% for the Petzval. From wkitty42 at windstream.net Fri Mar 6 13:19:44 2009 From: wkitty42 at windstream.net (waldo kitty) Date: Thu, 05 Mar 2009 23:19:44 -0500 Subject: [ATM] Star Images and Optical Components In-Reply-To: <0605BC2293114FCF861259DE42BAD7F3@MRBNOTEBOOK> References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com><0F1EAC818AD8499A85E44393CE11BE91@MRBNOTEBOOK> <001d01c99ddb$53620060$8f78fea9@amd> <0605BC2293114FCF861259DE42BAD7F3@MRBNOTEBOOK> Message-ID: <49B0A460.9010804@windstream.net> Jack Swaton @ Starry Host wrote: > Very good on the use of the camera, but the original suggestion (I thought) > was to use the camera as a diagnostic tool for various elements of the > optical train. If so, then how I am using it to that end? > > I may have TOTALLY missed the point of the use of the camera. you mean like seeing if the camera images the same "shadow" image that your eye sees? ;) if the camera sees it like your eye sees it, it would indicate something in the optical path setup... -- NOTE: NEW EMAIL ADDRESS!! _\/ (@@) Waldo Kitty, Waldo's Place USA __ooO_( )_Ooo_____________________ telnet://bbs.wpusa.dynip.com _|_____|_____|_____|_____|_____|_____ http://www.wpusa.dynip.com ____|_____|_____|_____|_____|_____|____ ftp://ftp.wpusa.dynip.com _|_Eat_SPAM_to_email_me!_YUM!__|_____ wkitty42 -at- windstream.net From tillerman1 at videotron.ca Fri Mar 6 13:28:16 2009 From: tillerman1 at videotron.ca (George Anderson) Date: Thu, 05 Mar 2009 23:28:16 -0500 Subject: [ATM] Star Images and Optical Components In-Reply-To: <8d3a545d0903050812p47fa14e4sd36fa85c3e2695ed@mail.gmail.com> References: <8d3a545d0903041851t656266f7gfa49ff885993651f@mail.gmail.com> <8d3a545d0903050709v5eb1d01i44ab62d6cc009d75@mail.gmail.com> <237C6AA1-925B-4954-A902-548F2F0FC2C3@psu.edu> <8d3a545d0903050812p47fa14e4sd36fa85c3e2695ed@mail.gmail.com> Message-ID: <49B0A660.50408@videotron.ca> I have the same problem, I am near sited with astigmatism. Without my glasses the dual images are there, with glasses on there is no problem. George Anderson Montreal Canada Clear skies and good health Stephen Koehler wrote: > Mike, > > >>> I don't know how common it is, but I definitely have this. It is only >>> noticeable at night on high-contrast, bright objects when my eyes are >>> dilated. >>> >> Have you by any chance had Lasik surgery? >> > > No, I haven't. In general, my eyes are pretty good--I have never had > to wear corrective lenses. Since about the age of 45, I have had to > use reading glasses more and more, but that's a different problem. > Since I don't wear glasses, I have not seen an eye specialist all that > often. However, the astigmatism was diagnosed when I was about 20. > > From webpub at fastmail.fm Fri Mar 6 21:44:48 2009 From: webpub at fastmail.fm (WebPub) Date: Fri, 6 Mar 2009 07:44:48 -0500 Subject: [ATM] Overlooked value of anRFT/Short F Ratio Newt Message-ID: <005c01c99e59$5731cfd0$ac58f804@Handsome> Shane LaPierre wrote: > Assuming a > typical off-axis image plane at 200X magnification (I'll find stats on > an eyepiece I have), I'd like to determine if coma is significant at > the edge. I suspect it can't be that bad @ f4.2 with magnifications > that high... then again I haven't run any numbers. It doesn't take much. In terms of ep AFOV semi-diameter "a" in degrees, sagittal coma in arc minutes is given by 3.75a/F^2, F being the mirror focal ratio number. This does imply that the angular apparent size of coma remains constant for given ep AFOV. But what really matters is its relative size with respect to the Airy disc, i.e. the wavefront error. In terms of the AFOV semi-diameter and ep. f.l. "f", it is given by W=af/1.5F^3 as the PV wavefront error at best focus, in units of 550nm wavelength. Taking a=20 degrees and F=4.2, gives the wavefront error as 3.6, 1.8 and 0.9 for the ep f.l. 20, 10 and 5 mm respectively. While sagittal coma remains unchanged angularly, both wavefront error and the degree of deformation of the diffraction pattern are significantly reduced in the 10mm and more so 5mm f.l. ep. This is why coma gradually vanishes from the outer field with the increase in magnification. Vlad From al at sgi.com Fri Mar 6 23:20:15 2009 From: al at sgi.com (Alexis Cousein) Date: Fri, 06 Mar 2009 15:20:15 +0100 Subject: [ATM] Overlooked value of an RFT / Short F Ratio Newt In-Reply-To: <003601c99ddc$e008aa40$8f78fea9@amd> References: <529F9DA5-7958-428D-AD13-E8901329DF0A@ct-astronomer.com><49AEBE6C.4040503@sgi.com> <6A762CB9-2E15-4DB2-9354-6E8F56B7A2D3@ct-astronomer.com> <003601c99ddc$e008aa40$8f78fea9@amd> Message-ID: <49B1311F.4030406@sgi.com> Bob May wrote: > With EPs of any particular AFOV, the coma at the edge of the > field should be the same, I think. The preceived angular size is. Of course, the ratio of the size of the comatic tails vs. the size of the central disk of the Airy diffraction pattern isn't constant, and once you use very high powers (e.g. exit pupils under 1mm) the main diffraction effects start to blur the coma (and ther object!) and makes the comatic tails less prominent. From al at sgi.com Fri Mar 6 23:44:12 2009 From: al at sgi.com (Alexis Cousein) Date: Fri, 06 Mar 2009 15:44:12 +0100 Subject: [ATM] Overlooked value of an RFT / Short F Ratio Newt In-Reply-To: <6A762CB9-2E15-4DB2-9354-6E8F56B7A2D3@ct-astronomer.com> References: <529F9DA5-7958-428D-AD13-E8901329DF0A@ct-astronomer.com> <49AEBE6C.4040503@sgi.com> <6A762CB9-2E15-4DB2-9354-6E8F56B7A2D3@ct-astronomer.com> Message-ID: <49B136BC.1040200@sgi.com> Shane LaPierre wrote: > This is the one I'd like to research the numbers on... Assuming a > typical off-axis image plane at 200X magnification (I'll find stats on > an eyepiece I have), I'd like to determine if coma is significant at the > edge. I suspect it can't be that bad @ f4.2 with magnifications that > high... It's certainly blatantly obvious in an f/4 Starblast at that magnification with an Ethos; I've tried it. It's even blatantly obvious in a 13mm Ethos in my f/4.5 scope (at 140x). The "diffraction limited" field (where coma is much less relevant than the diffraction by the aperture) is roughly 2mm wide on my f/4.5 scope (depending on the criterion you use - the one yielding 2mm isn't a particularly good one, but it gives you a ballpark figure). The field stop of a 13mm Ethos is 22mm wide... By the way, at very high powers, f/4.2 is uncomfortable for other reasons than merely coma. Many simple eyepiece designs will generate enough spherical aberration to degrade the wave front even on-axis. A Paracorr will hep even for that, because it makes the scope 15% slower as seen by the eyepiece. Obviously, a barlow also does (though the interplay with the amount of spherical aberration it generates and the amount it cancels in the eyepiece is far from simple in general). From shane at ct-astronomer.com Sat Mar 7 00:08:45 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Fri, 6 Mar 2009 10:08:45 -0500 Subject: [ATM] Overlooked value of an RFT / Short F Ratio Newt In-Reply-To: <49B136BC.1040200@sgi.com> References: <529F9DA5-7958-428D-AD13-E8901329DF0A@ct-astronomer.com> <49AEBE6C.4040503@sgi.com> <6A762CB9-2E15-4DB2-9354-6E8F56B7A2D3@ct-astronomer.com> <49B136BC.1040200@sgi.com> Message-ID: <3D118C1E-2BA8-4401-AFC2-2EC777E3F312@ct-astronomer.com> Thanks for your reply. It will be interesting to compare it to an f5.1 8" newt I have now. I also have a 20" f5 and have considered a new primary with an f4 ratio.... this new 8" f4.2 I made ought to give me a lot of personal experience to determine my own standards. No matter what, it sounds like a Paracorr is definitely on the list. Thanks for all the feedback on this thought, everybody. Shane On Mar 6, 2009, at 9:44 AM, Alexis Cousein wrote: > Shane LaPierre wrote: >> This is the one I'd like to research the numbers on... Assuming a >> typical off-axis image plane at 200X magnification (I'll find stats >> on an eyepiece I have), I'd like to determine if coma is >> significant at the edge. I suspect it can't be that bad @ f4.2 >> with magnifications that high... > > It's certainly blatantly obvious in an f/4 Starblast at that > magnification > with an Ethos; I've tried it. > > It's even blatantly obvious in a 13mm Ethos in my f/4.5 scope (at > 140x). > > The "diffraction limited" field (where coma is much less relevant than > the diffraction by the aperture) is roughly 2mm wide on my > f/4.5 scope (depending on the criterion you use - the one yielding 2mm > isn't a particularly good one, but it gives you a ballpark figure). > The > field stop of a 13mm Ethos is 22mm wide... > > By the way, at very high powers, f/4.2 is uncomfortable for other > reasons > than merely coma. Many simple eyepiece designs will generate enough > spherical aberration to degrade the wave front even on-axis. A > Paracorr > will hep even for that, because it makes the scope 15% slower as seen > by the eyepiece. Obviously, a barlow also does (though the interplay > with the amount of spherical aberration it generates and the amount > it cancels in the eyepiece is far from simple in general). > > From astroguy at nas.com Sat Mar 7 01:48:35 2009 From: astroguy at nas.com (astroguy at nas.com) Date: Fri, 6 Mar 2009 11:48:35 -0500 Subject: [ATM] Overlooked value of an RFT / Short F Ratio Newt Message-ID: <380-22009356164835243@M2W030.mail2web.com> In regards to the discussion on RFT scopes I use a 6" f/5 Mak-Newt and am completely sold on this scope and design. More often removed from the mounting and held in my lap while scanning the skies with a longer focus eyepiece than actually used on the mount. I would highly recommend this type of scope for those looking for both a challenge in ATM and for great observing. Kreig Original Message: ----------------- From: Shane LaPierre shane at ct-astronomer.com Date: Fri, 6 Mar 2009 10:08:45 -0500 To: atm at atmlist.net Subject: Re: [ATM] Overlooked value of an RFT / Short F Ratio Newt Thanks for your reply. It will be interesting to compare it to an f5.1 8" newt I have now. I also have a 20" f5 and have considered a new primary with an f4 ratio.... this new 8" f4.2 I made ought to give me a lot of personal experience to determine my own standards. No matter what, it sounds like a Paracorr is definitely on the list. Thanks for all the feedback on this thought, everybody. Shane On Mar 6, 2009, at 9:44 AM, Alexis Cousein wrote: > Shane LaPierre wrote: >> This is the one I'd like to research the numbers on... Assuming a >> typical off-axis image plane at 200X magnification (I'll find stats >> on an eyepiece I have), I'd like to determine if coma is >> significant at the edge. I suspect it can't be that bad @ f4.2 >> with magnifications that high... > > It's certainly blatantly obvious in an f/4 Starblast at that > magnification > with an Ethos; I've tried it. > > It's even blatantly obvious in a 13mm Ethos in my f/4.5 scope (at > 140x). > > The "diffraction limited" field (where coma is much less relevant than > the diffraction by the aperture) is roughly 2mm wide on my > f/4.5 scope (depending on the criterion you use - the one yielding 2mm > isn't a particularly good one, but it gives you a ballpark figure). > The > field stop of a 13mm Ethos is 22mm wide... > > By the way, at very high powers, f/4.2 is uncomfortable for other > reasons > than merely coma. Many simple eyepiece designs will generate enough > spherical aberration to degrade the wave front even on-axis. A > Paracorr > will hep even for that, because it makes the scope 15% slower as seen > by the eyepiece. Obviously, a barlow also does (though the interplay > with the amount of spherical aberration it generates and the amount > it cancels in the eyepiece is far from simple in general). > > _______________________________________________ ATM mailing list http://www.atmlist.net/ -------------------------------------------------------------------- myhosting.com - Premium Microsoft? Windows? and Linux web and application hosting - http://link.myhosting.com/myhosting From dlwebb at canit.se Sat Mar 7 03:02:45 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Fri, 6 Mar 2009 19:02:45 +0100 (MET) Subject: [ATM] Kepler telescope launches today Message-ID: Of general interest, this is the scope NASA has chosen to send into space to locate earth-like exoplanets, which launches today: http://www.nasa.gov/mission_pages/kepler/main/index.html Dominic From rflrs at rcn.com Sat Mar 7 04:20:47 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Fri, 06 Mar 2009 14:20:47 -0500 Subject: [ATM] Another Reuse In-Reply-To: <49B0981C.7010305@rcn.com> References: <49B0981C.7010305@rcn.com> Message-ID: <49B1778F.3030304@rcn.com> Richard F.L.R. Snashall wrote: > > http://users.rcn.com/rflrs/Ptz11-63x.atm ATMOS input file > http://users.rcn.com/rflrs/Ptz11-63x.len OSLO input file > http://users.rcn.com/rflrs/Ptz11-63x.txt TEXT prescription > http://users.rcn.com/rflrs/Ptz11-63x.zmx ZEMAX input file > > The unique feature here is that the modification actually > reduces the air-space of the primary doublet to zero. The > bonus here is that there is very little change in the F-C > longitudinal crossover zone -- from less than 85% for the > doublet to greater than 82% for the Petzval. However, if one is willing to accept a bigger shift, one could always start with a bit bluer doublet (152.4 mm f/12.8): http://users.rcn.com/rflrs/Ptz11-64b.atm ATMOS input file http://users.rcn.com/rflrs/Ptz11-64b.len OSLO input file http://users.rcn.com/rflrs/Ptz11-64b.txt TEXT prescription http://users.rcn.com/rflrs/Ptz11-64b.zmx ZEMAX input file And, then, removing the isoconvexity constraint of the secondary crown and being able to accept whatever lateral color error comes up (152.4 mm f/9.55): http://users.rcn.com/rflrs/Ptz11-64x.atm ATMOS input file http://users.rcn.com/rflrs/Ptz11-64x.len OSLO input file http://users.rcn.com/rflrs/Ptz11-64x.txt TEXT prescription http://users.rcn.com/rflrs/Ptz11-64x.zmx ZEMAX input file No, there is not a lot of residual lateral color here; in fact, it actually depends on how you measure it -- I did choose the secondary glasses for more than the cuteness being the same as the primary glasses. The key here, though, is that both the primary and secondary have no internal air-space. I have presented some Petzvals with no air-space in each doublet. In those, the corresponding doublet does not simultaneously correct both spherical aberration and coma in the green. From chaosopher23 at yahoo.com Sat Mar 7 05:48:58 2009 From: chaosopher23 at yahoo.com (Kevin MIchael Zabbo) Date: Fri, 6 Mar 2009 12:48:58 -0800 (PST) Subject: [ATM] I am about to drill a hole in my aluminum tube In-Reply-To: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> Message-ID: <8823.98875.qm@web33002.mail.mud.yahoo.com> Bad mistakes (I'm leaving the arithmetic out of this one, I wrote a program for it) can be covered up in any material if you use glue and fabric for the outside coating and inside flocking. I'm gluing black velvet to my tube inside and a bad star chart fabric to the outside of my tube to hide the terrible paint job and rough mess that the 10" PVC tube and aluminum flat stock has to offer the eyes. I'd be using Sonotube, but that stuff sucks up moisture. I'd be using fiberglass, but I'm not that good with it. I couldn't find any free aluminum tube, therefore, some cloth on PVC rules the day. Yes, the tube weighs 30 pounds... Kevin, Seeker of the Darkness --- On Sun, 3/1/09, Francis J. O'Reilly wrote: > From: Francis J. O'Reilly > Subject: [ATM] I am about to drill a hole in my aluminum tube > To: atm at atmlist.net > Cc: "Dick Parker" > Date: Sunday, March 1, 2009, 6:50 PM > I am about to drill an eyepiece hole in my aluminum tube, I > would like a check on my arithmetic computations. > > The mirror is 12.25 inches in diameter. The focal length is > 85 1/8 inches. The first surface of the mirror is 6 1/8 > inches from the back end of the tube. The 90 inch long > aluminum tube is somewhat oval, but not too bad. The > diameter where I will put the eyepiece is 15 1/8 inches. The > height of the two inch focuser is three inches. > > I come up with 81.75 inches from the back of the tube as > the center point of the eyepiece hole. > > I would appreciate any thoughts on this matter. I made a > bad mistake with a prior tube abd I would like to avoid any > further probelms. > > Thank you. > > Francis J. O'Reilly > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From chaosopher23 at yahoo.com Sat Mar 7 06:06:40 2009 From: chaosopher23 at yahoo.com (Kevin MIchael Zabbo) Date: Fri, 6 Mar 2009 13:06:40 -0800 (PST) Subject: [ATM] Parfocal Cass-Greg program C++ source code In-Reply-To: <00be01c98d41$c01b6020$40522060$@net> Message-ID: <511617.72112.qm@web33001.mail.mud.yahoo.com> This program I wrote makes the math a bit easier when designing a parfocal Cassegrainian and Gregorian using different secondary holders on the same primary mirror that has a b = -1. It will not work with an aplanatic system such as the R-C, and it will not Gregorianize the R-C (possible) to work with the multiple secondaries. Here it is, in source code. You might have to do a little programming to make it work perfectly, but it works great on my system: // Cassgreg v.0.1 // First Version // Computes a Cassegrainian telescope with a parfocal Gregorian telescope // using the Back Focal Length as its point of reference // "How far does the focal point stick out of the back of the primary mirror?" // is the same for both the Cass and the Greg in this program. // So, if you can work to close tolerances, you can have a Cass and Greg on one primary mirror! // // Please read through the program before compiling // // General Public License - Copy and distribute with source code and all included files // Please send donation if you're generous and would like to buy me beer // Payment optional of course, this is really supposed to be free stuff // I collect foreign currency, too. // contact me at kevinmzabbo at yahoo.com and I'll try to help you with problems you might have // or tell you where to send the beer money // // No guarantees and I'm not responsible if this messes your computer up. It didn't mess mine up when I wrote it. // // Source Code for casscalc should compile on any computer equipped with a C++ compiler // Read the comments so you know what to comment/uncomment for your operating system // Written on a Celeron A-333 running Slackware 10.2 with 2.6.13 testing phase kernel // // On Linux, compile using this command: // g++ cassgreg.cpp -o cassgreg // // For DOS users, do this: // c++ cassgreg.cpp -o cassgreg.exe or cpp cassgreg.cpp -o cassgreg.exe // On some truly antiquated systems, the exe tag is important. This program should work in the // 8.3 World. It might even run on a Mac with a C++ compiler. Don't ask me how to // make one of those work. If you have one, you probably know how to do it. // // Now the fun part: #include #include #include //#include int intro(); //Who, why, what... you know. int getstuff(); //The program needs data. Tell it what it wants to hear. int domath(); //You did your math homework, right? using namespace std; char dimension[40]; //Tell the computer what measurement system you're using: inches, feet, miles, parsecs... dimension is simply a string that does not affect the outcome of the program. //YES, I like globals. They are used throughout. Why pass what you can store? float DDP, DDScass, DDSgreg, b1, b2cass, b2greg, rocP, rocScass, rocSgreg, gcass, ggreg, ep, es, BFL, pcass, pgreg, ppcass, ppgreg, Fcass, Fgreg, f1, FDS, B, A, dcass, dgreg, eCass, eGreg ; // I think I got them all // where: // DDP is the diameter of the primary. Input value // DDS is the diameter of the secondary. Calculated value // b1 is the conic constant of the primary. Could be calculated or input. // b2 is the conic constant of the secondary. Calculated value. // rocP is the radius of curvature of the primary. 2 x f1, calculated from input f1 // rocS is the radius of curvature of the secondary. Calculated value. // gcass and ggreg, gamma, the ratio of the focal length of the primary and focal length of the whole system. Calculated. // ep and es are sagittae of the respective mirrors. Calculated value. // BFL is Back Focal Length. Input value. // pcass and pgreg is the distance the secondary lies from the prime focus. Calculated value. // ppcass and ppgreg is the distance the secondary lies from the system focus. Calculated value. // Fcass and Fgreg is the system focal length. Input value. // f1 is the primary focal length. Input value. // FDS is the system focal ratio, an input value. // B is the off-axis coma. Calculated value. To be implemented later. // A is astigmatism. Calculated value. To be implemented later. // d is the distance the secondary lies from the primary. Calculated value. // eCass and eGreg are sagittas of the secondary mirrors. main() { // DOS users uncomment the next line to clear the screen. Comment it back if your compiler burps. // clrscr(); // DOS users comment this line out: system("clear"); intro(); //Who, why, what... you know. getstuff(); //The program needs data. Tell it what it wants to hear. domath(); //You did your math homework, right? return 0; } int intro() { cout <<" Thank you for compiling cassgreg. I wrote it for amateur telescope makers in " << endl; cout <<" hopes that it would be useful and good for designing a parfocal Cassegrainian and Gregorian" << endl; cout <<" telescope. This program will tell you all the dimensions you will need to get that" << endl; cout <<" glass ground and polished to the right dimensions and tell you how far apart to" << endl; cout <<" mount the mirrors from each other. While tolerances are not given, it is best to"<> dimension; cout <<" What is the optical diameter of your primary mirror? " ; cin >> DDP; // Absolute values used and converted later cout <<" What is the desired system focal ratio F for the Cassegrainian? " ; cin >> Fcass; Fcass = fabs(Fcass); cout <<" What is the desired system focal ratio F for the Gregorian? " ; cin >> Fgreg; Fgreg = fabs(Fgreg); cout <<" What is the primary focal length? "; cin >> f1; cout << " Back focal length is the distance from the primary mirror surface the focal length sticks out." << endl; cout << " 12 inches is a good number. (Small and negative values place the system focus in Coude variety.)" << endl; cout << " What is the Back Focal Length? "; cin >> BFL; // Texereau gives this number as 'e' which is also used as sagitta. I use BFL to avoid // any confusion with formula 2.10.1 cout <<" What is the conic constant of the primary mirror?" << endl; cout <<" Enter -1 for paraboloid, which is a true Cassegrainian or Gregorian. " ; cin >> b1; return 0; } int domath() { // Filler Variables not passed on! float Xcass, Xgreg, Zcass, Zgreg; float YCass, YGreg; // X is a number raised to an exponent // For some reason, the compiler likes to keep it simple in the pow(X, Y) function. // Key Formula, 6.1, not a numbered formula: gcass = Fcass / (f1 / DDP); // Cass version, already made a positive number at input time ggreg = (Fgreg * -1) / (f1 / DDP); // Changes F to a negative number // Secondary position p formula, 6.5.1: pcass = ((f1 + BFL) / (gcass + 1)); pgreg = ((f1 + BFL) / (ggreg + 1)); // Secondary distance from the primary (Derived formula) dcass = pcass * gcass; dgreg = pgreg * ggreg; // Radius of Curvature of the Secondary, formula 6.5.3: rocScass = -1 * ((2 * pcass * gcass) / (gcass - 1)); // Cass rocSgreg = -1 * ((2 * pgreg * ggreg) / (ggreg - 1)); // Greg // Diameter of the Secondary DDScass = ((DDP * pcass) / f1 ); DDSgreg = fabs((DDP * pgreg) / f1 ); // Computes the value b2 of a True Cassegrainian or Gregorian using values already provided // using formula 6.6.1 on page 137, not considering if it is a true cass-greg or not. // This program assumes that the telescope will be built around its primary mirror. // There is no option to input the secondary b. rocP = f1 * 2; Xcass = (gcass / (gcass - 1)); Xgreg = (ggreg / (ggreg - 1)); Zcass = ((gcass + 1) / (gcass - 1)); Zgreg = ((ggreg + 1) / (ggreg - 1)); b2cass = (1 + b1) * ( rocP / (rocP - (2 * dcass))) * ( pow(Xcass, 3)) - ((pow(Zcass, 2))); b2greg = (1 + b1) * ( rocP / (rocP - (2 * dgreg))) * ( pow(Xgreg, 3)) - ((pow(Zgreg, 2))); //Sagittas YCass = (DDScass / 2); YGreg = (DDSgreg / 2); eCass = (pow(YCass, 2) / (2 * rocScass)); eGreg = (pow(YGreg, 2) / (2 * rocSgreg)); // Display the results // Uncomment after it works right system("clear"); // DOS users uncomment this line and comment the above line out // clrscr(); cout.setf(ios::showpoint); cout << " True Cassegrainian results Gregorian Results" << endl; cout << " With values given, all dimensions in " << dimension << ":" << endl; cout << " System Focal Ratio Desired " << Fcass << setw(39) << Fgreg << endl; cout << " Primary focal length " << f1 << " " << endl; cout << " Primary Radius of Curvature " << rocP << endl; cout << " Back Focal Length " << BFL << endl; cout << " and conic constant of the primary " << b1 << endl; cout << " The telescope looks like this: " << endl; cout << " Secondary to Primary Distance = " << dcass - BFL << setw(39) << dgreg - BFL << endl; cout << " Secondary Conic Constant = " << b2cass << setw(39) << b2greg << endl; cout << " Secondary Sagitta = " << eCass << setw(39) << eGreg << endl; cout << " Secondary Radius of Curvature = " << rocScass << setw(39) << rocSgreg << endl; cout << " Diameter of the secondary = "<< DDScass << setw(39) << DDSgreg << endl; return 0; } From chaosopher23 at yahoo.com Sat Mar 7 06:11:57 2009 From: chaosopher23 at yahoo.com (Kevin MIchael Zabbo) Date: Fri, 6 Mar 2009 13:11:57 -0800 (PST) Subject: [ATM] Newtonian Diagonal Position program C++ source code Message-ID: <522022.64779.qm@web33006.mail.mud.yahoo.com> This is a revised version of Tex's Newtonian diagonal position formula. This one includes the thickness of the primary and its holder and measures from the end of the tube and also includes an offset value for recessed primary holders. This one tells you where to drill the eyepiece hole. Here's the source code: // Newtonian Diagonal Mirror Calculation Program // Uses information from Jean Texereau's "How to Make a Telescope" // General Public License, generic version. // Program written by Kevin Zabbo, Seeker of the Darkness // Additional equations and numbers added by me, such as: // Primary Cell height is now considered as part of the tube length // Primary thickness is now considered // Primary distance from cell is also considered // Can be compiled anywhere a C++ compiler lives. // You may have to comment the screen clearing utilities out to make it work right. // It won't clear the screen before it works if you do that, but it will run. // I don't know the screen clearing utility on a Mac, f'rinstance, and I don't expect it to run // on a VAX or something weird. DO NOT run it on a HAL-9000! // Written on an old Celeron with Slackware 10.2 Linux running 2.6.13 kernel. // Should work on anything 386 and up // Now the fun stuff #include #include int intro(); int getstuff(); int domath(); int seestuff(); using namespace std; // YES, I like globals! The whole thing uses them, why do extra work of passing variable values? float a, adelta, aa, l, K, L, M, N, d, DD, f, e, r, RR, delta, tube, focuser, prithick, cellthick, x, xoffset; char dimension[40]; /* Where: a = the small dimension of the diagonal mirror aa = large dimension of the diagonal mirror l = how far from the primary focal plane the secondary mirror lies L = Calculated Variable M = Calculated Variable N = Calculated Variable d = Size of the full moon at focus, .009 x focal length DD = Diameter of the primary f = focal length e = sagitta RR = Radius of Curvature delta = Diagonal Offset Value tube = tube diameter focuser = focuser height average of rack in height and rack out height, which should accommodate all eyepieces prithick = primary mirror thickness cellthick = height of the cell x = calculated variable involving prithick and cellthick xoffset = input value, distance primary back is from the end of the tube dimension is what to call the dimensions given Glue thickness holding the primary to the cell is negligible. */ main() { // DOS users uncomment the following line: // clrscr(); // DOS users comment this line out: system("clear"); intro(); getstuff(); domath(); seestuff(); return 0; } int intro() //Who, what, why, how... { cout << "This is that Diagonal Mirror Size and Position Calculator you've been waiting for." << endl; cout << "Uses equations and data from Jean Texereau's How to Make a Telescope with additions" << endl; cout << "made by the programmer, Kevin Zabbo, Seeker of the Darkness." << endl; cout << "These additions give you the options to input the primary cell height, primary thickness" << endl; cout << "and an offset, which will give you an easier way to find where to drill your hole." << endl; cout << "Written in general for those constructing a Newtonian Telescope." << endl; cout << "This program also tells the Offset Value as well as the Simple Value." << endl; // Comment out the following lines if you think they are annoying. cout << "If you like it and you think I'm deserving a donation, please send beer money." << endl; cout << "Email chaosopher23 at yahoo.com and I'll tell you where to send it." << endl; cout << "Though the program is GPL and free, donations are accepted. I also collect" << endl; cout << "foreign currency for display in my scrapbook." << endl; return 0; } int getstuff() // input section { // Commented out because I'm using them as globals // float a, L, M, N, d, DD, f, e, r, RR, delta; cout << endl; // Determine what to call the dimensions given to the program cout << " What measurements are you using, inches, millimeters, parsecs... ?"<< endl; cin >> dimension; cout << " Please tell me a few things about your telescope." << endl; cout << " What is the primary diameter?"<< endl; cin >> DD; cout << " What is the focal length of your mirror?" << endl; cin >> f; cout << " What is the tube outside diameter?" << endl; cin >> tube; cout << " How tall is your focuser, average of rack in and rack out heights?" << endl; cin >> focuser; cout << " How thick is the primary mirror?" << endl; cin >> prithick; cout << " How tall is the mirror cell?" << endl; cin >> cellthick; cout << " How far is the primary cell from the back of the telescope?" << endl; cin >> xoffset; return 0; } int domath() // Numbers Cereal, keep on crunching! { //Commented out because I'm using globals //float a, L, M, N, d, DD, f, e, r, RR, delta; K = abs(((tube / 2) + focuser) - f); //Position of the secondary from primary l = abs(((tube / 2) + focuser)); // Position of the secondary from focus // K + l = f d = .009 * f; // Size of the full moon at focus e = ((DD/2)*(DD/2)) / (2 * (f*2)); // Sagitta of the primary L = (d * (f - e)) + (l*(DD - d)); // L, M, N are calculation variables M = (2 * (f - e)) - ( DD - d ); N = (2 * (f - e)) + ( DD - d ); a = (((DD - d) * l) / f); adelta = (L / M) + (L / N); // The Small dimension of the diagonal mirror, offset version aa = a ; // The Big dimension of the diagonal mirror, offset version delta = (( L / M ) - ( L / N )) / 2; x = K + cellthick + prithick; return 0; } int seestuff() // Don't tell a psychiatrist you see stuff. This section is the output. { // Make it pretty later cout << "The results:" << endl; cout << "distance diagonal mirror lies from focal plane... "<< l << " " << dimension << endl; cout << "Size of the full moon in the focal plane......... " << d << " " << dimension << endl; cout << "Sagitta of the primary mirror.................... "<< e << " " << dimension <<0F1EAC818AD8499A85E44393CE11BE91@MRBNOTEBOOK> <001d01c99ddb$53620060$8f78fea9@amd> <0605BC2293114FCF861259DE42BAD7F3@MRBNOTEBOOK> Message-ID: <002801c99ea6$1517a280$8f78fea9@amd> Jack, basically, the use of a camera is to replace the eye in any testing. The testing of individual components of the telescope is also easily done with the camera. The Foucault test works very well with a camera behind the KE as you can take the time to place the camera properly (best is to have the KE support carry the camera so it doesn't move as you adjust the KE for getting the shadows) as the image is nice and steady so you can see it without having to hole your head rigid behind hte KE. Flats need to have a reference flat to obtain fringes against and the camera is very sensitive to the contrast of hte fringes. Finally, you can also, as we've been discussing, do he star test wiht a camera and thus obtain a record of what things look like and you can do a nice detailed record of what is happening rather than the quick fleeting observation by the eye. Also, the ince thing about using a camera is that you can not only keep a record of what is seen but also discuss the image with others to obtain a better idea of what is happening. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From burrjaw at earthlink.net Sat Mar 7 09:31:53 2009 From: burrjaw at earthlink.net (Jim Burrows) Date: Fri, 06 Mar 2009 16:31:53 -0800 Subject: [ATM] Diffract with rainbow. Message-ID: As thought about earlier, I have reprogrammed Diffract so that when you click "White" it works 3 FFTs for the three primary colors: Red, Green, and Blue to simulate doing the tests with a white source. Some of the tests, e.g. a narrow slit, really get quite colorful. Download as usual: http://home.earthlink.net/~burrjaw/public/diffract.zip (2009-03-06, Win32, 387.2 k) -- Jim Burrows -- http://home.earthlink.net/~burrjaw -- mailto:burrjaw at earthlink.net -- Seattle N47.4723 W122.3662 (WGS84) From tcohen at blakeglobal.com Sun Mar 8 15:52:58 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Sat, 7 Mar 2009 22:52:58 -0800 Subject: [ATM] astigmatism correction In-Reply-To: <6F4CC628F40246F0AB6836CB24DD7679@BLAKESF.LOCAL> References: <381308.25919.qm@web31006.mail.mud.yahoo.com><577AFF371DAD476096F8EF9E907BD471@BLAKESF.LOCAL> <6F4CC628F40246F0AB6836CB24DD7679@BLAKESF.LOCAL> Message-ID: By aggressively attacking the astigmatism, I have been able to remove about 90-95% of it with only a very small localized blemish in the form of a narrow depression of small extent. What remains is visible very close to the COC by a solitary fringe displaying an "S" pattern. I'll see if the remainder of the astig comes out by itself, as I still have to finish up removing what remains of the oblate spheroid problem. The edge looks fine as far as I can tell. I'll post an updated photo in a couple of days. From jhm.vangastel at ziggo.nl Sun Mar 8 18:09:32 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Sun, 8 Mar 2009 10:09:32 +0100 Subject: [ATM] first measurements References: <49264954.8050509@tularosa.net> <271447C9-213B-40B6-916D-8DC5142DFDFF@psu.edu> Message-ID: <83E256B4DE91479FAA3E13F52591557A@niks03981037eb> Today, after 75 minutes of figuring (W-stroke, 2/3 overhang) my 8" f/3.85 mirror, I took the first Foucault measurements. Alle zones corrected between 61 and 65%, except for the 3rd zone: only 31%. Without the mask I also saw a very slight high center, but it is small and under the secondary. No sign of a turned edge. I think I have some 'lucky stroke', because in my former mirrors I also never had one. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ From jhm.vangastel at ziggo.nl Sun Mar 8 18:14:43 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Sun, 8 Mar 2009 10:14:43 +0100 Subject: [ATM] first measurements References: <49264954.8050509@tularosa.net> <271447C9-213B-40B6-916D-8DC5142DFDFF@psu.edu> <83E256B4DE91479FAA3E13F52591557A@niks03981037eb> Message-ID: <730A8F73BDEA4CB9A5FB739AFEDAD00A@niks03981037eb> Forgot to mention that I use a 6-zone mask. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Jan van Gastel" To: "ATM list" Sent: Sunday, March 08, 2009 10:09 Subject: [ATM] first measurements > Today, after 75 minutes of figuring (W-stroke, 2/3 overhang) my 8" f/3.85 > mirror, I took the first Foucault measurements. Alle zones corrected > between 61 and 65%, except for the 3rd zone: only 31%. > > Without the mask I also saw a very slight high center, but it is small and > under the secondary. > > No sign of a turned edge. I think I have some 'lucky stroke', because in > my former mirrors I also never had one. > > Jan > http://members.ziggo.nl/jhm.vangastel/Astronomy/ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From till.theegarten at yahoo.de Sun Mar 8 22:14:30 2009 From: till.theegarten at yahoo.de (Till Theegarten) Date: Sun, 8 Mar 2009 14:14:30 +0100 Subject: [ATM] Borofloat in Zemax Catalogue References: <000701c8f801$ed8b8a60$c8a29f20$@theegarten@yahoo.de> <489A1BB2.2060409@rcn.com> <489B2C75.9070707@rcn.com> Message-ID: <000d01c99fef$d1217240$736456c0$@theegarten@yahoo.de> Hello, I am modelling with Zemax for a Lurie. To try the corrector plate made of Borofloat (this Is currently the only payable glass I could get in the size of 12.5" ) I am looking for parameters to enter in Zemax. I cannot find a page where all parameters are shown, no matter which formula to use (Sellmeier, Schott....). Does anybody have a catalogue where Borofloat is entered or can give me a self made catalogue with Borofloat in it? Thanks Till From richard at foucault.co.uk Sun Mar 8 23:37:56 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Sun, 8 Mar 2009 14:37:56 +0000 Subject: [ATM] Borofloat in Zemax Catalogue In-Reply-To: <000d01c99fef$d1217240$736456c0$@theegarten@yahoo.de> References: <000701c8f801$ed8b8a60$c8a29f20$@theegarten@yahoo.de> <489A1BB2.2060409@rcn.com> <489B2C75.9070707@rcn.com> <000d01c99fef$d1217240$736456c0$@theegarten@yahoo.de> Message-ID: <536311452.20090308143756@foucault.co.uk> Hello Till, Sunday, March 8, 2009, 1:14:30 PM, you wrote: > Hello, > I am modelling with Zemax for a Lurie. To try the corrector plate made of > Borofloat Best fit to published values, using Schott formula : A0 : 2.32956383E+000 A1 : -1.37067549E-001 A2 : -1.01019271E-001 A3 : 3.16726194E-002 A4 : -4.42170849E-003 A5 : 2.42760083E-004 -- Best regards, Richard in the UK From hermit at outofoptions.org Mon Mar 9 00:33:06 2009 From: hermit at outofoptions.org (hermit) Date: Sun, 08 Mar 2009 11:33:06 -0400 Subject: [ATM] first measurements In-Reply-To: <83E256B4DE91479FAA3E13F52591557A@niks03981037eb> References: <49264954.8050509@tularosa.net> <271447C9-213B-40B6-916D-8DC5142DFDFF@psu.edu> <83E256B4DE91479FAA3E13F52591557A@niks03981037eb> Message-ID: <49B3E532.8090500@outofoptions.org> Jan van Gastel wrote: > (W-stroke, 2/3 overhang) ??????? Overhang and not total stroke length? Ken Lowther From burrjaw at earthlink.net Mon Mar 9 09:06:16 2009 From: burrjaw at earthlink.net (Jim Burrows) Date: Sun, 08 Mar 2009 17:06:16 -0700 Subject: [ATM] first measurements In-Reply-To: <83E256B4DE91479FAA3E13F52591557A@niks03981037eb> References: <49264954.8050509@tularosa.net> <271447C9-213B-40B6-916D-8DC5142DFDFF@psu.edu> <83E256B4DE91479FAA3E13F52591557A@niks03981037eb> Message-ID: At 2009-03-08 10:09 +0100, Jan van Gastel wrote: >Today, after 75 minutes of figuring (W-stroke, 2/3 overhang) my 8" >f/3.85 mirror, I took the first Foucault measurements. Alle zones >corrected between 61 and 65%, except for the 3rd zone: only 31%. Jan, Post your readings so we can have fun trying to decipher them (Foucault is tough at f/3.85). Say whether fixed or moving source, and give the inner/outer zone radii. -- Jim Burrows -- http://home.earthlink.net/~burrjaw -- mailto:burrjaw at earthlink.net -- Seattle N47.4723 W122.3662 (WGS84) From jhm.vangastel at ziggo.nl Mon Mar 9 16:02:16 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Mon, 9 Mar 2009 08:02:16 +0100 Subject: [ATM] first measurements References: <49264954.8050509@tularosa.net> <271447C9-213B-40B6-916D-8DC5142DFDFF@psu.edu> <83E256B4DE91479FAA3E13F52591557A@niks03981037eb> Message-ID: <1DBA97F3C6834F62B059DE0845B343CE@niks03981037eb> Hi Jim, I already did some more work: a total of four figuring sessions. First one 75 minutes (with some cold pressing after 20 minutes), one 20 minutes session and two 15 minutes sessions. I cured the hill at the center by (a) 3/8 diameter overhang W-stroke instead of 1/3 and (b) a narrower W for the center zones. This had effect but not enough. Therefore, in the fourth session I used still more overhang and did a very narrow W for the center zones. After the third session zone 6 also lagged behind, so I also made a narrower W for the edge zones (almost COC) in the same session, which cured the edge zone. I use a moving source Foucault tester. Last readings (in millimeters) are: 0.00, 0.41, 0.66, 1.11, 1.57, 2.01, so zone 3 is lagging behind. Think I will use a narrower W in zone 3 now, do also a bit more work at the center in the next session and make my session 10 minutes. The zone radii (left out the center for the secondary): Mirror Diameter = 204 mm Mirror Radius = 102 mm COC = 1571 mm. The center 9% of the mirror area is excluded Zone Inner Outer Corrected Center # Radius Radius Radius ----- --------- --------- --------- 1 30.6000 mm 50.1428 mm 40.9584 mm 2 50.1428 mm 63.9706 mm 57.2658 mm 3 63.9706 mm 75.3006 mm 69.7507 mm 4 75.3006 mm 85.1359 mm 80.2936 mm 5 85.1359 mm 93.9471 mm 89.5957 mm 6 93.9471 mm 102.0000 mm 98.0149 mm Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Jim Burrows" To: "ATM list" Sent: Monday, March 09, 2009 1:06 Subject: Re: [ATM] first measurements > At 2009-03-08 10:09 +0100, Jan van Gastel wrote: > >>Today, after 75 minutes of figuring (W-stroke, 2/3 overhang) my 8" >>f/3.85 mirror, I took the first Foucault measurements. Alle zones >>corrected between 61 and 65%, except for the 3rd zone: only 31%. > > Jan, > > Post your readings so we can have fun trying to decipher them > (Foucault is tough at f/3.85). Say whether fixed or moving source, > and give the inner/outer zone radii. > > -- Jim Burrows > -- http://home.earthlink.net/~burrjaw > -- mailto:burrjaw at earthlink.net > -- Seattle N47.4723 W122.3662 (WGS84) > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From behambu at artinso.com Mon Mar 9 22:03:35 2009 From: behambu at artinso.com (Berthold Hamburger) Date: Mon, 9 Mar 2009 14:03:35 +0100 Subject: [ATM] grit and pitch suppliers Message-ID: <017101c9a0b7$78d23070$6a769150$@com> Hi, After many years I am getting back to grinding and would like to know whether somebody can recommend suppliers for grinding grit and pitch in Europe and preferably Spain. Thanks Berthold -- Berthold Hamburger - Cellist/Spain Email: behambu at artinso.com http://www.artinso.com http://www.astro.artinso.com From dlwebb at canit.se Mon Mar 9 22:40:02 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Mon, 9 Mar 2009 14:40:02 +0100 (MET) Subject: [ATM] grit and pitch suppliers In-Reply-To: <017101c9a0b7$78d23070$6a769150$@com> Message-ID: On Mon, 9 Mar 2009, Berthold Hamburger wrote: > Hi, > > > > After many years I am getting back to grinding and would like to know > whether somebody can recommend suppliers for grinding grit and pitch in > Europe and preferably Spain. Larger SiC up to about #600 (average particle ~17 micron) can be had from a number of abrasives suppliers one can find in local phone book. I still get the fine SiC (#600- #1200) and CeO from Microabrasives Corp in MA, USA. They did not take small orders previously, but the past few years I have been ordering boxes of several sizes at a time directly from them. I do not know if Microabrasives sells pitch. My purchases have always worked out, but they have historically ignored email, so I call in my orders when in the States. For the moment, they have been laying off people, so patience needed: http://www.masslive.com/news/index.ssf/2009/02/micro_abrasives_corp_in_westfi.html?category=Business&category=Westfield Some people order from gotgrit.com. Prices at the time I checked were higher than Microabrasives, but Gotgrit has pitch (mirror kits???) that can be ordered at same time. Dominic From dlwebb at canit.se Mon Mar 9 23:45:53 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Mon, 9 Mar 2009 15:45:53 +0100 (MET) Subject: [ATM] Star Images and Optical Components In-Reply-To: <63B90775AEAD45C0AC7CA1BB2BD86ED7@MRBNOTEBOOK> Message-ID: On Thu, 5 Mar 2009, Jack Swaton @ Starry Host wrote: > Dominic, > OK, so I can try and dig out the old webcam and do (or not) remove the lens, > but then what? What am I trying to do? Take a picture to post for others to > diagnose? What? > > Thanks, > Jack I think retracing some steps, it was discussed whether this comes from eyes or optical system. Camera gives you another set of eyes to compare against. I have removed at least one double image, which was actually I suspect lateral color, by adding an aperture stop. Eye and camera sensed this. Dominic From dlwebb at canit.se Mon Mar 9 23:48:56 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Mon, 9 Mar 2009 15:48:56 +0100 (MET) Subject: [ATM] Star Images and Optical Components In-Reply-To: <49B0A660.50408@videotron.ca> Message-ID: On Thu, 5 Mar 2009, George Anderson wrote: > I have the same problem, I am near sited with astigmatism. Without my > glasses the dual images are there, with glasses on there is no problem. > > George Anderson > Montreal Canada Wow, my reading says this kind of double vision is not very common, but clearly there is no hardship in finding people that have it. Since I have diplopia myself, I am currently learning how to treat it, and apparently it is treatable. Dominic From ncain at frontier.co.uk Tue Mar 10 01:05:08 2009 From: ncain at frontier.co.uk (Nicholas Cain) Date: Mon, 9 Mar 2009 16:05:08 -0000 Subject: [ATM] grit and pitch suppliers References: <017101c9a0b7$78d23070$6a769150$@com> Message-ID: <00b001c9a0d0$d19e1610$510811ac@corp.frontier.co.uk> In the UK I've used Beacon Hill Telescopes; http://www.beaconhilltelescopes.cwc.net/ That was quite a while ago, but it's still on their price list. Nik ----- Original Message ----- From: "Berthold Hamburger" To: Sent: Monday, March 09, 2009 1:03 PM Subject: [ATM] grit and pitch suppliers > Hi, > > > > After many years I am getting back to grinding and would like to know > whether somebody can recommend suppliers for grinding grit and pitch in > Europe and preferably Spain. > > > > Thanks > > > > Berthold > > > > -- > > Berthold Hamburger - Cellist/Spain > > Email: behambu at artinso.com > > http://www.artinso.com > > http://www.astro.artinso.com > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From jack.swaton at starryhost.com Tue Mar 10 01:50:47 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Mon, 9 Mar 2009 09:50:47 -0700 Subject: [ATM] Star Images and Optical Components In-Reply-To: References: <63B90775AEAD45C0AC7CA1BB2BD86ED7@MRBNOTEBOOK> Message-ID: Interesting! Where was the aperture stop? At the base of the focuser in the draw tube? Or did you put a baffle in the OTA? Jack -----Original Message----- From: Dominic-Luc Webb [mailto:dlwebb at canit.se] Sent: Monday, March 09, 2009 7:46 AM To: Jack Swaton @ Starry Host Cc: 'ATM Superheros' Subject: RE: [ATM] Star Images and Optical Components On Thu, 5 Mar 2009, Jack Swaton @ Starry Host wrote: > Dominic, > OK, so I can try and dig out the old webcam and do (or not) remove the lens, > but then what? What am I trying to do? Take a picture to post for others to > diagnose? What? > > Thanks, > Jack I think retracing some steps, it was discussed whether this comes from eyes or optical system. Camera gives you another set of eyes to compare against. I have removed at least one double image, which was actually I suspect lateral color, by adding an aperture stop. Eye and camera sensed this. Dominic From scotte12 at gmail.com Tue Mar 10 12:27:43 2009 From: scotte12 at gmail.com (Scott Ewart) Date: Mon, 9 Mar 2009 23:27:43 -0400 Subject: [ATM] I am about to drill a hole in my aluminum tube In-Reply-To: <49AC25EE.1080605@windstream.net> References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> <49AC25EE.1080605@windstream.net> Message-ID: <056401c9a130$2d147f70$873d7e50$@com> Does anyone know where I can find the latest version of Newt? I have an older version and would like to update. I can't find it with Google (maybe I'm not asking nice enough). Thanks. Scott Ewart -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of waldo kitty Sent: Monday, March 02, 2009 1:31 PM To: Francis J. O'Reilly; atm at atmlist.net Subject: Re: [ATM] I am about to drill a hole in my aluminum tube this last one, focuser to front of tube, is what you are trying to calculate whereas NEWT uses it as a set input... in my toying around, i tend to place the focuser the same distance from the front of the tube as the mirror face is from the back of the tube... the result of this is that NEWT calcs the focuser hole to be 73.937 inches from the mirror face (first surface?)... that plus the mirror face to the back of the tube gives me 80.062 inches... that puts my result 1.688 inches shorter then yours and i don't have a clue where that difference may have come from... From hermit at outofoptions.org Tue Mar 10 12:35:40 2009 From: hermit at outofoptions.org (hermit) Date: Mon, 09 Mar 2009 23:35:40 -0400 Subject: [ATM] I am about to drill a hole in my aluminum tube In-Reply-To: <056401c9a130$2d147f70$873d7e50$@com> References: <79C5837257DF49FC9517EF33EFC9F960@HELENYLCMWAV95> <49AC25EE.1080605@windstream.net> <056401c9a130$2d147f70$873d7e50$@com> Message-ID: <49B5E00C.9080600@outofoptions.org> http://www.dalekeller.net/ATM/newtonians/newtsoft/newtsoft.htm Scott Ewart wrote: > Does anyone know where I can find the latest version of Newt? I > have an older version and would like to update. I can't find it with Google > (maybe I'm not asking nice enough). Thanks. > > Scott Ewart > > > -----Original Message----- > From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of > waldo kitty > Sent: Monday, March 02, 2009 1:31 PM > To: Francis J. O'Reilly; atm at atmlist.net > Subject: Re: [ATM] I am about to drill a hole in my aluminum tube > > > this last one, focuser to front of tube, is what you are trying to calculate > > whereas NEWT uses it as a set input... in my toying around, i tend to place > the > focuser the same distance from the front of the tube as the mirror face is > from > the back of the tube... the result of this is that NEWT calcs the focuser > hole > to be 73.937 inches from the mirror face (first surface?)... that plus the > mirror face to the back of the tube gives me 80.062 inches... that puts my > result 1.688 inches shorter then yours and i don't have a clue where that > difference may have come from... > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From scotte12 at gmail.com Tue Mar 10 13:06:50 2009 From: scotte12 at gmail.com (Scott Ewart) Date: Tue, 10 Mar 2009 00:06:50 -0400 Subject: [ATM] astigmatism question In-Reply-To: <002001c99cb5$d32523d0$796f6b70$@de> References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL><974920.36609.qm@web54501.mail.re2.yahoo.com><73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> <005a01c99c77$47d5b940$8f78fea9@amd> <2A8743AE2D0649EEB22403A744BDA47F@piv555a133b59e> <002001c99cb5$d32523d0$796f6b70$@de> Message-ID: <056b01c9a135$a415cac0$ec416040$@com> This is absolutely not true. I've see this written here before and I just don't understand how others would have any trouble seeing it. I didn't use a Couder mask, but used a pin stick instead. With a simple knife edge test or Ronchi test close to focus (basically the same as knife edge), it was very obvious to me when I started to get astigmatism while figuring my 12.4". It may have been worse at first when I did first notice something was wrong, but once I knew what I was seeing and knew what to look for, it was not hard at all to see. It made it possible for me to figure out what my real 3D shape was and how to attack it. There were times the center looked good but the edges were crooked and vice-versa. And when it was gone, I KNEW it was gone. The only time you can't see it is if the astig is a perfect potato chip shape and one of its axes happens to land exactly vertical on the test stand. You're not going to see anything if you regularly use a mask and never look at the whole surface. But in addition to my zonal readings, the ability to see the whole surface at once with a Ronchi was invaluable. When the numbers were right AND the Ronchi showed smooth curves, I knew I was done. Scott Ewart -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Jeremy Royston Sent: Wednesday, March 04, 2009 5:42 AM To: atm at atmlist.net Subject: [ATM] astigmatism question Foucault and Ronchi tests are unsuitable for detecting and measuring astigmatism, they won't see it unless it is extreme From baldjeff at comcast.net Tue Mar 10 13:15:47 2009 From: baldjeff at comcast.net (Jeff Baldwin) Date: Mon, 9 Mar 2009 21:15:47 -0700 Subject: [ATM] astigmatism question References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL><974920.36609.qm@web54501.mail.re2.yahoo.com><73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> <005a01c99c77$47d5b940$8f78fea9@amd> <2A8743AE2D0649EEB22403A744BDA47F@piv555a133b59e><002001c99cb5$d32523d0$796f6b70$@de> <056b01c9a135$a415cac0$ec416040$@com> Message-ID: I think that the multitude of ways to check for astigmatism allows each of us to use whichever way we like. If you can easily see it on the foucault test, go for it, if you like using a ball or false star, use that, if you like star testing, use that. Some of us really don't like using the ronchi or foucault to astig test, so we don't. Some of us do. It's great that there's many ways to skin a cat. Bald Jeff and Glenda Baldwin Lathrop, CA www.agetawaylogcabin.com www.stocktonastro.org > This is absolutely not true. I've see this written here before and > I just don't understand how others would have any trouble seeing it. > > > Scott Ewart > > > > Foucault and Ronchi tests are unsuitable for > detecting and measuring astigmatism, they won't see it unless it is > extreme > From atmpob at yahoo.com Tue Mar 10 13:58:38 2009 From: atmpob at yahoo.com (Dale Eason) Date: Mon, 9 Mar 2009 21:58:38 -0700 (PDT) Subject: [ATM] astigmatism question In-Reply-To: <056b01c9a135$a415cac0$ec416040$@com> Message-ID: <447923.53959.qm@web54506.mail.re2.yahoo.com> Foucault and Ronchi tests are more sensitive at showing the effect of astig at longer F ratios. What F ratio was your mirror? Dale Eason --- On Mon, 3/9/09, Scott Ewart wrote: > From: Scott Ewart > Subject: Re: [ATM] astigmatism question > To: atm at atmlist.net > Date: Monday, March 9, 2009, 11:06 PM > This is absolutely not true. I've see this written here > before and > I just don't understand how others would have any > trouble seeing it. I > didn't use a Couder mask, but used a pin stick instead. > With a simple knife > edge test or Ronchi test close to focus (basically the same > as knife edge), > it was very obvious to me when I started to get astigmatism > while figuring > my 12.4". . From jroyston at gmx.de Tue Mar 10 18:09:27 2009 From: jroyston at gmx.de (Jeremy Royston) Date: Tue, 10 Mar 2009 10:09:27 +0100 Subject: [ATM] astigmatism question In-Reply-To: <056b01c9a135$a415cac0$ec416040$@com> References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL><974920.36609.qm@web54501.mail.re2.yahoo.com><73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> <005a01c99c77$47d5b940$8f78fea9@amd> <2A8743AE2D0649EEB22403A744BDA47F@piv555a133b59e> <002001c99cb5$d32523d0$796f6b70$@de> <056b01c9a135$a415cac0$ec416040$@com> Message-ID: <001501c9a15f$eaf0bb60$c0d23220$@de> Hello all, I seem to have drawn some flak with my statement Perhaps I should have qualified it a bit. If the axis of the astigmatism cylinder is near parallel to the Ronchi grating lines you won't see any asymmetry. If it's near perpendicular you'll see some assymmetry - the shadow lines are slightly tilted with respect to the Ronchi grid lines I still maintain that the Ronchi and Foucault tests are unsuitable for MEASURING astigmatism. In this case the Hartmann 2D and interferometer tests deliver reliable and quantitative results (apart from support distortion) You can see the effect of astigmatism with the program Diffract (from Jim Burrows, simulate Foucault, Ronchi tests etc.) and Aberrator (simulate star and planet images) Best wishes, Jerry -----Urspr?ngliche Nachricht----- Von: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] Im Auftrag von Scott Ewart Gesendet: Dienstag, 10. M?rz 2009 05:07 An: atm at atmlist.net Betreff: Re: [ATM] astigmatism question This is absolutely not true. I've see this written here before and I just don't understand how others would have any trouble seeing it ... snip Scott Ewart -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Jeremy Royston Sent: Wednesday, March 04, 2009 5:42 AM To: atm at atmlist.net Subject: [ATM] astigmatism question Foucault and Ronchi tests are unsuitable for detecting and measuring astigmatism, they won't see it unless it is extreme _______________________________________________ From gfbrandenburg at yahoo.com Tue Mar 10 19:42:52 2009 From: gfbrandenburg at yahoo.com (Guy Brandenburg) Date: Tue, 10 Mar 2009 03:42:52 -0700 (PDT) Subject: [ATM] astigmatism question Message-ID: <889265.96482.qm@web111514.mail.gq1.yahoo.com> A few years ago, there was a mirror-testing round robin on this list, in which quite a few experienced mirror-makers tested three different mirrors on their own, sent in their results to a central person without letting anybody else know, and then shipped off the box to the next person on the list. At the end, the results were announced, as well as the results of an interferogram. One of the mirrors was somewhat astigmatic. NOT ONE of us ronchi- or foucault- testers caught that. Guy Brandenburg, Washington, DC My home page on astronomy, mathematics, education: http://home.earthlink.net/~gfbranden/GFB_Home_Page.html or else http://tinyurl.com/r6fh2 ============================= "Education isn't rocket science. It's much, much harder." (Author unknown) --- On Tue, 3/10/09, Scott Ewart wrote: > From: Scott Ewart > Subject: Re: [ATM] astigmatism question > To: atm at atmlist.net > Date: Tuesday, March 10, 2009, 12:06 AM > ??? This is absolutely > not true.? I've see this written here before and > I just don't understand how others would have any trouble > seeing it.? I > didn't use a Couder mask, but used a pin stick > instead.? With a simple knife > edge test or Ronchi test close to focus (basically the same > as knife edge), > it was very obvious to me when I started to get astigmatism > while figuring > my 12.4". > ??? It may have been worse at first when I > did first notice something > was wrong, but once I knew what I was seeing and knew what > to look for, it > was not hard at all to see.? It made it possible for > me to figure out what > my real 3D shape was and how to attack it.? There were > times the center > looked good but the edges were crooked and > vice-versa.? And when it was > gone, I KNEW it was gone.? The only time you can't see > it is if the astig is > a perfect potato chip shape and one of its axes happens to > land exactly > vertical on the test stand. > ??? You're not going to see anything if you > regularly use a mask and > never look at the whole surface.? But in addition to > my zonal readings, the > ability to see the whole surface at once with a Ronchi was > invaluable.? When > the numbers were right AND the Ronchi showed smooth curves, > I knew I was > done. > > Scott Ewart > > > -----Original Message----- > From: atm-bounces at atmlist.net > [mailto:atm-bounces at atmlist.net] > On Behalf Of > Jeremy Royston > Sent: Wednesday, March 04, 2009 5:42 AM > To: atm at atmlist.net > Subject: [ATM] astigmatism question > > Foucault and Ronchi tests are unsuitable for > detecting and measuring astigmatism, they won't see it > unless it is extreme > > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From wa4guu at verizon.net Tue Mar 10 19:51:39 2009 From: wa4guu at verizon.net (Jerry) Date: Tue, 10 Mar 2009 06:51:39 -0400 Subject: [ATM] astigmatism question In-Reply-To: <001501c9a15f$eaf0bb60$c0d23220$@de> Message-ID: I'm with Scott on this. Foucault and Ronchi tests are not as unreliable as is widely believed. There is more to be seen in those shadows and bent bands than some ATM's realize. Look hard. Jerry -----Original Message----- Scott Ewart astigmatism question This is absolutely not true. I've see this written here before and I just don't understand how others would have any trouble seeing it ... snip Scott Ewart -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Jeremy Royston Sent: Wednesday, March 04, 2009 5:42 AM To: atm at atmlist.net Subject: [ATM] astigmatism question Foucault and Ronchi tests are unsuitable for detecting and measuring astigmatism, they won't see it unless it is extreme From dlwebb at canit.se Tue Mar 10 20:06:00 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Tue, 10 Mar 2009 12:06:00 +0100 (MET) Subject: [ATM] Star Images and Optical Components In-Reply-To: Message-ID: On Mon, 9 Mar 2009, Jack Swaton @ Starry Host wrote: > Interesting! > Where was the aperture stop? At the base of the focuser in the draw tube? Or > did you put a baffle in the OTA? > > Jack Specifically, it is a refractor, a spotting scope. It has an ~86 mm diameter objective with a green coating. There is a built-in zoom eyepiece stating 20x-60x at 80 mm. The aperture stop is home made from thin posterboard-like cardboard material. The aperture stop is about 20 mm diameter and centered on optical axis. It is placed in front of the objective. Seeing a clear success, I made a 15 mm aperture stop as well. That performs better still, focus is remarkably sharp, but too dim for most observing. I reackoned it might be useful for solar or lunar observing. For solar viewing, I have a Baader filter in front of the aperture stop, so most sunlight never enters the system. Weather here in Sweden is not favorable this time of year, but recently was able to look through the clouds. Focus with zoom to 60X was crisp. An interesting point is that this spotting scope was quite cheap. When I tested it in the shop, I thought I might be able to improve it with an aperture stop and plan worked. I plan to take pictures when time and weather become favorable. Dominic From nilsolof.carlin at telia.com Wed Mar 11 04:03:06 2009 From: nilsolof.carlin at telia.com (Nils Olof Carlin) Date: Tue, 10 Mar 2009 20:03:06 +0100 Subject: [ATM] astigmatism question References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL><974920.36609.qm@web54501.mail.re2.yahoo.com><73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> <005a01c99c77$47d5b940$8f78fea9@amd> <2A8743AE2D0649EEB22403A744BDA47F@piv555a133b59e><002001c99cb5$d32523d0$796f6b70$@de> <056b01c9a135$a415cac0$ec416040$@com> Message-ID: Using Ronchi or Foucault as Texereau describes it (with steel ball) is easy on a spherical mirror - no doubt at all. But detecting a significant astig on a figured, near-paraboloid (not to mention fast) mirror is something very different! To get an idea of what you're up to, try Jim Burrows' Diffract - identifying the intended astig term is difficult, but at least you are told the RMS error directly. You'll be surprised at the amount of astig that is not obvious at all... Nils Olof ----- Original Message ----- From: "Scott Ewart" To: Sent: Tuesday, March 10, 2009 5:06 AM Subject: Re: [ATM] astigmatism question > This is absolutely not true. I've see this written here before and > I just don't understand how others would have any trouble seeing it. I > didn't use a Couder mask, but used a pin stick instead. With a simple > knife > edge test or Ronchi test close to focus (basically the same as knife > edge), > it was very obvious to me when I started to get astigmatism while figuring > my 12.4". > It may have been worse at first when I did first notice something > was wrong, but once I knew what I was seeing and knew what to look for, it > was not hard at all to see. It made it possible for me to figure out what > my real 3D shape was and how to attack it. There were times the center > looked good but the edges were crooked and vice-versa. And when it was > gone, I KNEW it was gone. The only time you can't see it is if the astig > is > a perfect potato chip shape and one of its axes happens to land exactly > vertical on the test stand. > You're not going to see anything if you regularly use a mask and > never look at the whole surface. But in addition to my zonal readings, > the > ability to see the whole surface at once with a Ronchi was invaluable. > When > the numbers were right AND the Ronchi showed smooth curves, I knew I was > done. > > Scott Ewart From rmay at nethere.com Wed Mar 11 05:34:28 2009 From: rmay at nethere.com (Bob May) Date: Tue, 10 Mar 2009 12:34:28 -0800 Subject: [ATM] astigmatism question References: <7157FF332C2040F8B9A8BA0566A9AFC0@BLAKESF.LOCAL><974920.36609.qm@web54501.mail.re2.yahoo.com><73F6E7787468415FAD9CC2E8ECEC60DF@BLAKESF.LOCAL> <005a01c99c77$47d5b940$8f78fea9@amd> <2A8743AE2D0649EEB22403A744BDA47F@piv555a133b59e> <002001c99cb5$d32523d0$796f6b70$@de><056b01c9a135$a415cac0$ec416040$@com> <001501c9a15f$eaf0bb60$c0d23220$@de> Message-ID: <001001c9a1bf$9d509820$8f78fea9@amd> I'll agree with you that actually measuring how bad astig. is with the Ronchi or Foucault test is basically not easily possible. Hoever, you can indeed detect any astig. of importance with those tests. I've found tha detecting it is quite easy with the Ronchi test but, since I've not gone through the math needed to quantify it, all I will know is that it does exist and does need to be eliminated. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From peter at kitgear.com Wed Mar 11 06:46:16 2009 From: peter at kitgear.com (Peter) Date: Tue, 10 Mar 2009 17:46:16 -0400 Subject: [ATM] astigmatism question In-Reply-To: <001001c9a1bf$9d509820$8f78fea9@amd> Message-ID: Could you also check for astigmatism using the Foucault test if you look for a tilt in the shadows? Is there a downside to checking this way? Thanks, From s.c.koehler at gmail.com Wed Mar 11 07:28:42 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Tue, 10 Mar 2009 17:28:42 -0500 Subject: [ATM] astigmatism question In-Reply-To: References: <001001c9a1bf$9d509820$8f78fea9@amd> Message-ID: <8d3a545d0903101528j4e0018a9re78936786afd56ae@mail.gmail.com> To elaborate a little on what Guy posted, here is Scott Rynchovsky's summary of the astigmatism in round robin mirror C: Mirror C 6" F5.4 Typical numbers from Foucault testers: 1/14 wave Peak-to-valley, ca. 1/50 - 1/90 wave RMS Correction about right. Strehl ~ 0.98 Narrow TDE, could be masked. Mirror rated excellent to outstanding by most reviewers. Interferometry (Roger): 1/17 wave RMS; Strehl 87% correction P-V ~ 1/13 wave Astigmatism increases RMS error significantly. Strehl (James) ~ 0.86 Mirror C showed astigmatism, ca. 0.2 wave P-V, which accounts for roughly half of the surface error. Only one of the Foucault testers (Hanagan) considered the astigmatism of mirror C explicitly, but found no evidence of it in an eyepiece test. He did detect strain in a cross-polarizer test on the blank. I have repeated both test on mirror C. Under some conditions I could detect a modest "cross" of strain similar to the image in Texereau (p. 155, Figure 70, type II). In a ROC eyepiece test I can detect astigmatism when I am looking for it, but it is very faint and I only see it outside of focus as the inside of focus pattern is washed out due to the spherical correction. It is less dramatic than the 0.37 wave astigmatism example in Suiter, p. 260. Modest astigmatism is not easily detected without interferometry analysis. A 6" f/5.4 is not an especially fast or large mirror. Admittedly, the amount of astigmatism is not large, but it's probably at the level you would like to detect and correct. None of the Foucault testers detected it. If this were a larger or faster mirror, the difficulty of detection would increase dramatically. As an aside, Dale Eason and I got a chance (after the round robin was complete) to attempt to use a holographic null test (like a Foucault test, but with a strange, striped mask on the mirror), to detect the astigmatism. It was pretty visible using that test. Essentially, we used a computer-generated hologram (i.e., strange paper mask) to remove the SA, so we could perform a Foucault test as if the mirror were spherical, where the tilted line of astigmatism can be seen relatively easily. Here's my message announcing our results: http://astro.umsystem.edu/atm/ARCHIVES/FEB05/msg00063.html Here's an archived copy of Mauritz Andersson's page describing the holographic null test. Unfortunately, neither the pictures, nor the script to generate a mask are in the archive. http://web.archive.org/web/20080126204948/http://www.kvac.uu.se/~mauritz/holomask/ -- Steve Koehler From scotte12 at gmail.com Wed Mar 11 09:02:30 2009 From: scotte12 at gmail.com (Scott Ewart) Date: Tue, 10 Mar 2009 20:02:30 -0400 Subject: [ATM] astigmatism question In-Reply-To: <447923.53959.qm@web54506.mail.re2.yahoo.com> References: <056b01c9a135$a415cac0$ec416040$@com> <447923.53959.qm@web54506.mail.re2.yahoo.com> Message-ID: <05d801c9a1dc$acd1fdd0$0675f970$@com> Dale, It was f/5.5. I guess that's in the medium range. I suppose it's true that the broader the shadow (gray zone), the easier to see. I refigured my 13.1" f/4.5 Coulter mirror as well and I remember having some mild astig problems with that, too. Like I said, once you know what to look for, it isn't hard to see. It can look like a slight yin-yang pattern in the center, or just a little skewing at the top and bottom. Scott -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Dale Eason Sent: Tuesday, March 10, 2009 12:59 AM To: atm at atmlist.net Subject: Re: [ATM] astigmatism question Foucault and Ronchi tests are more sensitive at showing the effect of astig at longer F ratios. What F ratio was your mirror? Dale Eason --- On Mon, 3/9/09, Scott Ewart wrote: > From: Scott Ewart > Subject: Re: [ATM] astigmatism question > To: atm at atmlist.net > Date: Monday, March 9, 2009, 11:06 PM > This is absolutely not true. I've see this written here > before and > I just don't understand how others would have any > trouble seeing it. I > didn't use a Couder mask, but used a pin stick instead. > With a simple knife > edge test or Ronchi test close to focus (basically the same > as knife edge), > it was very obvious to me when I started to get astigmatism > while figuring > my 12.4". . _______________________________________________ ATM mailing list http://www.atmlist.net/ From atmpob at yahoo.com Wed Mar 11 09:55:16 2009 From: atmpob at yahoo.com (Dale Eason) Date: Tue, 10 Mar 2009 17:55:16 -0700 (PDT) Subject: [ATM] astigmatism question In-Reply-To: <05d801c9a1dc$acd1fdd0$0675f970$@com> Message-ID: <430008.62442.qm@web54501.mail.re2.yahoo.com> http://www.atmlist.net/contrib/atmpob-at-yahoo-dot-com/100LPIRonchi_Astig_Simulations2.jpg ? The above is a simulation of various mirrors with different astig values.? The values are? PV on the surface.? The 1/8 value would be diffraction limited if there are no other errors.? The 1/4 wave would need to be removed to be a better mirror.? Notice the 1/4 wave can be very subtle on the 16 F5 mirror.? It is not impossible to see but it would be subtle in real life.? If left the strehl ratio for that mirror is .7. ? All images not labled as sphere are Parabaloid.? The ronchi screen is 100 LPI.? The offsets go inside ROC to outside ROC (left to right). ? Dale Eason From atmpob at yahoo.com Wed Mar 11 10:34:24 2009 From: atmpob at yahoo.com (Dale Eason) Date: Tue, 10 Mar 2009 18:34:24 -0700 (PDT) Subject: [ATM] astigmatism question In-Reply-To: <430008.62442.qm@web54501.mail.re2.yahoo.com> Message-ID: <730905.99337.qm@web54501.mail.re2.yahoo.com> http://www.atmlist.net/contrib/atmpob-at-yahoo-dot-com/astig_foucault.jpg ? Foucault simulation of astig 45 deg to knife.? It is much more difficult to see in Fouculat test I think.?The 1 wave PV astig looks pretty normal to me.? ? The Ronchi astig orientation was also 45 deg to the horizontal axis.?As others have said if it is oriented to the axis of the knife or lines then it can not be seen at all. ? All of these images were computed by my program OpenFringe normally used to analyze interferograms.? You can find a copy on the Yahoo group Interferometry in the Files section. ? Dale Eason ? From jhm.vangastel at ziggo.nl Wed Mar 11 21:23:12 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Wed, 11 Mar 2009 13:23:12 +0100 Subject: [ATM] what to do best? References: <446404.49074.qm@web54109.mail.re2.yahoo.com> Message-ID: <2C0EA6F9809F4D5486411811AD73B2F5@niks03981037eb> I parabolizing my 204 mm f/3.85. Edge correction is to much. What is the best way to reduce the edge correction? See http://members.ziggo.nl/jhm.vangastel/Astronomy/xp.htm Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ From melockwo at uiuc.edu Thu Mar 12 01:11:12 2009 From: melockwo at uiuc.edu (Mike Lockwood) Date: Wed, 11 Mar 2009 10:11:12 -0600 Subject: [ATM] astigmatism question In-Reply-To: <730905.99337.qm@web54501.mail.re2.yahoo.com> References: <730905.99337.qm@web54501.mail.re2.yahoo.com> Message-ID: <49B7E2A0.6050708@uiuc.edu> Hi, With Foucault, astigmatism is best spotted when the mirror is near spherical. At that stage, small amounts are visible if the mirror is rotated such that the astig axes are 45 degrees from the knife edge. With an artificial star test, you can check for astig before, during, and after figuring. As you roll the return image through focus different zones of the mirror will come to focus, and you can watch for "roundness". Also, if you support the mirror poorly for testing, you will see the effects. Personally I've never managed to put astig in a mirror during figuring (by machine or hand). If that is happening, then the figuring technique needs to be examined, unless you're trying to figure a toroid. Dale Eason wrote: > http://www.atmlist.net/contrib/atmpob-at-yahoo-dot-com/astig_foucault.jpg > Foucault simulation of astig 45 deg to knife. It is much more > difficult to see in Fouculat test I think. The 1 wave PV astig looks > pretty normal to me. You need to bring the simulated knife edge farther in and cut off more simulated light. Then take another "look". It should show up as at top/bottom asymmetry. > The Ronchi astig orientation was also 45 deg to the horizontal axis. > As others have said if it is oriented to the axis of the knife or > lines then it can not be seen at all. Ignorance is bliss, right? If you can't see it, it must not be there.... :) Mike Lockwood From melockwo at uiuc.edu Thu Mar 12 01:13:43 2009 From: melockwo at uiuc.edu (Mike Lockwood) Date: Wed, 11 Mar 2009 10:13:43 -0600 Subject: [ATM] what to do best? In-Reply-To: <2C0EA6F9809F4D5486411811AD73B2F5@niks03981037eb> References: <446404.49074.qm@web54109.mail.re2.yahoo.com> <2C0EA6F9809F4D5486411811AD73B2F5@niks03981037eb> Message-ID: <49B7E337.8000800@uiuc.edu> Jan, Jan van Gastel wrote: > I parabolizing my 204 mm f/3.85. Edge correction is to much. What is the > best way to reduce the edge correction? > See http://members.ziggo.nl/jhm.vangastel/Astronomy/xp.htm That much transverse error is a big problem. First, verify that your measurements were not in error. If they are good, then I'd recommend migrating back toward a sphere until the correction on that zone gets back to ~50-60%, and then try to take the figuring to completion. Correcting the outer zone is the hardest part of figuring fast mirrors, so if you know what you did to get there, you're ahead of the game. Mike Lockwood From al at sgi.com Thu Mar 12 01:32:54 2009 From: al at sgi.com (Alexis Cousein) Date: Wed, 11 Mar 2009 17:32:54 +0100 Subject: [ATM] astigmatism question In-Reply-To: <730905.99337.qm@web54501.mail.re2.yahoo.com> References: <730905.99337.qm@web54501.mail.re2.yahoo.com> Message-ID: <49B7E7B6.3010601@sgi.com> Dale Eason wrote: > The 1 wave PV astig looks pretty normal to me. It's harder to see on these "static" images than it is to see on a real moving shadow. From jhm.vangastel at ziggo.nl Thu Mar 12 02:31:58 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Wed, 11 Mar 2009 18:31:58 +0100 Subject: [ATM] what to do best? References: <446404.49074.qm@web54109.mail.re2.yahoo.com> <2C0EA6F9809F4D5486411811AD73B2F5@niks03981037eb> <49B7E337.8000800@uiuc.edu> Message-ID: Hi Mike, I already thought this would be the way to go, but I hoped there would be a shortcut. The overcorrected edge was a remainder of a mistake I made some parabolization sessions ago and I hoped I would 'discover' an easy way to get get rid of it, while working on the rest of the mirror's surface. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Mike Lockwood" To: "ATMList" Cc: "Jan van Gastel" Sent: Wednesday, March 11, 2009 17:13 Subject: Re: [ATM] what to do best? > Jan, > > Jan van Gastel wrote: >> I parabolizing my 204 mm f/3.85. Edge correction is to much. What is the >> best way to reduce the edge correction? >> See http://members.ziggo.nl/jhm.vangastel/Astronomy/xp.htm > > That much transverse error is a big problem. > > First, verify that your measurements were not in error. > > If they are good, then I'd recommend migrating back toward a sphere until > the correction on that zone gets back to ~50-60%, and then try to take the > figuring to completion. > > Correcting the outer zone is the hardest part of figuring fast mirrors, so > if you know what you did to get there, you're ahead of the game. > > Mike Lockwood From atmpob at yahoo.com Thu Mar 12 10:47:37 2009 From: atmpob at yahoo.com (Dale Eason) Date: Wed, 11 Mar 2009 18:47:37 -0700 (PDT) Subject: [ATM] astigmatism question In-Reply-To: <000e01c9a2a9$66bf5e00$eb5ef804@Handsome> Message-ID: <929110.7775.qm@web54506.mail.re2.yahoo.com> Vladimir sacek sent me the email below.? I tried to reply to him but it bounced.?? ? I use the Y zernike term for atsitg and adjust it until?the?worst case PV on?a surface profile graphs is as stated in the images.??Then use the?rule that 1/8 wave PV on the surface (1/4 wave on the??wavefront) is a good approximation for?diffraction limited. ?Does that help explain my statements and under those assumptions are my statements correct? ? Dale Eason? --- On Wed, 3/11/09, vladimir sacek wrote: From: vladimir sacek Subject: Re: [ATM] astigmatism question To: "Dale Eason" Date: Wednesday, March 11, 2009, 7:27 PM (off list) Hope you don't mind; I've sent reply to the list earlier today, which has never made it. Some glitch with new email account that seems to be working well with everyone else. Visual simulations, like those you posted, are the best way to get to the core of this. But there are some numerical inconsistencies. Since surface astigmatism doubles in the wavefront, and the PV-to-RMS ratio for primary astigmatism is sq.rt.24, "diffraction limited" PV (based on 0.0745 diffraction-limited RMS error in units of the wavelength) is 0.365 on the wavefront, and half as much on the surface. Regards, Vladimir Sacek From atmpob at yahoo.com Thu Mar 12 14:03:37 2009 From: atmpob at yahoo.com (Dale Eason) Date: Wed, 11 Mar 2009 22:03:37 -0700 (PDT) Subject: [ATM] astigmatism question In-Reply-To: <002001c9a2c0$16953eb0$155af804@Handsome> Message-ID: <943178.63396.qm@web54504.mail.re2.yahoo.com> Once more I get the following error when using yahoo (my email system) to send mail to Vlad sacek. ----------------- Hi. This is the qmail-send program at yahoo.com. I'm afraid I wasn't able to deliver your message to the following addresses. This is a permanent error; I've given up. Sorry it didn't work out. : Sorry, I couldn't find any host named coppert.net. (#5.1.2) ------------------------------------------------------------- >>my response to Vlad Thank you Vlad, I did not realize the 1/4 rule only applied to SA. I should have however. I will update the pictures I posted earlier in a few days. This time I used OpenFringe to modify the Y astig zernike value until the RMS value was .075 and sure enough the PV astig value was .365. Thank you for correcting me. Dale Eason --- On Wed, 3/11/09, vladimir sacek wrote: > From: vladimir sacek > Subject: Re: [ATM] astigmatism question > To: atmpob at yahoo.com > Date: Wednesday, March 11, 2009, 10:10 PM > If Y is the Zernike aberration term for primary astigmatism, > it can be written as: > > Y= z?24(cos2?-0.5)?2 = A(cos2?-0.5)?2 > > where "z" is usually termed Zernike expansion > coefficient, "A" is the peak aberration > coefficient for primary astigmatism (equaling 1/2 the P-V > wavefront error), "?" is the > pupil angle and "?" is the height in the pupil > normalized to 1 for pupil radius. Setting ? > to 0 and ? to 1, gives the maximum aberration value (along > the axis of aberration) as > > Y= 0.5z?24 = A/2 > > with "z" effectively equaling the RMS wavefront > error. As you know, diffraction limited > RMS - regardless of the type of aberration - is 0.0745 in > units of the wavelength (exactly > 1/?180). The corresponding peak aberration coefficient - > and PV - is thus A=0.0745?24 > or 0.365, also in the units of the wavelength. > > Diffraction limited PV wavefront for coma is 0.42 wave, and > so on. The 0.25 wave PV is > "diffraction limited" only for primary spherical > aberration. > > Vlad > > ----- Original Message ----- From: "Dale Eason" > > To: > Sent: Wednesday, March 11, 2009 9:47 PM > Subject: Re: [ATM] astigmatism question > > > Vladimir sacek sent me the email below. I tried to reply to > him but it bounced. > > I use the Y zernike term for atsitg and adjust it until the > worst case PV on a surface profile graphs is as stated in > the images. Then use the rule that 1/8 wave PV on the > surface (1/4 wave on the wavefront) is a good approximation > for diffraction limited. Does that help explain my > statements and under those assumptions are my statements > correct? > > Dale Eason > > --- On Wed, 3/11/09, vladimir sacek > wrote: > > From: vladimir sacek > Subject: Re: [ATM] astigmatism question > To: "Dale Eason" > Date: Wednesday, March 11, 2009, 7:27 PM > > (off list) > > Hope you don't mind; I've sent reply to the list > earlier today, which > has never made it. > Some glitch with new email account that seems to be working > well with everyone > else. > > Visual simulations, like those you posted, are the best way > to get to the core > of this. > But there are some numerical inconsistencies. Since surface > astigmatism doubles > in the > wavefront, and the PV-to-RMS ratio for primary astigmatism > is sq.rt.24, > "diffraction > limited" PV (based on 0.0745 diffraction-limited RMS > error in units of the > wavelength) > is 0.365 on the wavefront, and half as much on the surface. > > Regards, > > Vladimir Sacek > > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > > -------------------------------------------------------------------------------- > > > > No virus found in this incoming message. > Checked by AVG - www.avg.com > Version: 8.0.237 / Virus Database: 270.11.9/1992 - Release > Date: 03/09/09 19:20:00 From al at sgi.com Thu Mar 12 16:54:26 2009 From: al at sgi.com (Alexis Cousein) Date: Thu, 12 Mar 2009 08:54:26 +0100 Subject: [ATM] astigmatism question In-Reply-To: <929110.7775.qm@web54506.mail.re2.yahoo.com> References: <929110.7775.qm@web54506.mail.re2.yahoo.com> Message-ID: <49B8BFB2.3010709@sgi.com> Dale Eason wrote: > Vladimir sacek sent me the email below. I tried to reply to him but it bounced. > > I use the Y zernike term for atsitg and adjust it until the worst case PV on a surface profile > graphs is as stated in the images. Then use the rule that 1/8 wave PV on the surface > (1/4 wave on the wavefront) is a good approximation for diffraction limited. That's a bit off because that rule of thumb had spherical aberration in mind. Astigmatism has a smaller RMS error for the wavefront for a given PTV error. From vla at copper.net Thu Mar 12 21:02:13 2009 From: vla at copper.net (vladimir sacek) Date: Thu, 12 Mar 2009 08:02:13 -0400 Subject: [ATM] astigmatism question References: <943178.63396.qm@web54504.mail.re2.yahoo.com> Message-ID: <004b01c9a30a$62c41d70$f34ef804@Handsome> Think I fixed the error (an extra letter somehow got into the "sender address"). Correction to my email: > "A" is the peak aberration coefficient for primary astigmatism > (equaling 1/2 the P-V wavefront error)... "A" equals the PV error. Vla ----- Original Message ----- From: "Dale Eason" To: Sent: Thursday, March 12, 2009 1:03 AM Subject: Re: [ATM] astigmatism question > > > Once more I get the following error when using yahoo (my email system) to > send mail to Vlad sacek. > > ----------------- > Hi. This is the qmail-send program at yahoo.com. > I'm afraid I wasn't able to deliver your message to the following > addresses. > This is a permanent error; I've given up. Sorry it didn't work out. > > : > Sorry, I couldn't find any host named coppert.net. (#5.1.2) > ------------------------------------------------------------- > > > >>>my response to Vlad > Thank you Vlad, > > I did not realize the 1/4 rule only applied to SA. I should have however. > I will update the pictures I posted earlier in a few days. > > This time I used OpenFringe to modify the Y astig zernike value until the > RMS value was .075 and sure enough the PV astig value was .365. Thank you > for correcting me. > > Dale Eason > > > --- On Wed, 3/11/09, vladimir sacek wrote: > >> From: vladimir sacek >> Subject: Re: [ATM] astigmatism question >> To: atmpob at yahoo.com >> Date: Wednesday, March 11, 2009, 10:10 PM >> If Y is the Zernike aberration term for primary astigmatism, >> it can be written as: >> >> Y= z?24(cos2?-0.5)?2 = A(cos2?-0.5)?2 >> >> where "z" is usually termed Zernike expansion >> coefficient, "A" is the peak aberration >> coefficient for primary astigmatism (equaling 1/2 the P-V >> wavefront error), "?" is the >> pupil angle and "?" is the height in the pupil >> normalized to 1 for pupil radius. Setting ? >> to 0 and ? to 1, gives the maximum aberration value (along >> the axis of aberration) as >> >> Y= 0.5z?24 = A/2 >> >> with "z" effectively equaling the RMS wavefront >> error. As you know, diffraction limited >> RMS - regardless of the type of aberration - is 0.0745 in >> units of the wavelength (exactly >> 1/?180). The corresponding peak aberration coefficient - >> and PV - is thus A=0.0745?24 >> or 0.365, also in the units of the wavelength. >> >> Diffraction limited PV wavefront for coma is 0.42 wave, and >> so on. The 0.25 wave PV is >> "diffraction limited" only for primary spherical >> aberration. >> >> Vlad >> >> ----- Original Message ----- From: "Dale Eason" >> >> To: >> Sent: Wednesday, March 11, 2009 9:47 PM >> Subject: Re: [ATM] astigmatism question >> >> >> Vladimir sacek sent me the email below. I tried to reply to >> him but it bounced. >> >> I use the Y zernike term for atsitg and adjust it until the >> worst case PV on a surface profile graphs is as stated in >> the images. Then use the rule that 1/8 wave PV on the >> surface (1/4 wave on the wavefront) is a good approximation >> for diffraction limited. Does that help explain my >> statements and under those assumptions are my statements >> correct? >> >> Dale Eason >> >> --- On Wed, 3/11/09, vladimir sacek >> wrote: >> >> From: vladimir sacek >> Subject: Re: [ATM] astigmatism question >> To: "Dale Eason" >> Date: Wednesday, March 11, 2009, 7:27 PM >> >> (off list) >> >> Hope you don't mind; I've sent reply to the list >> earlier today, which >> has never made it. >> Some glitch with new email account that seems to be working >> well with everyone >> else. >> >> Visual simulations, like those you posted, are the best way >> to get to the core >> of this. >> But there are some numerical inconsistencies. Since surface >> astigmatism doubles >> in the >> wavefront, and the PV-to-RMS ratio for primary astigmatism >> is sq.rt.24, >> "diffraction >> limited" PV (based on 0.0745 diffraction-limited RMS >> error in units of the >> wavelength) >> is 0.365 on the wavefront, and half as much on the surface. >> >> Regards, >> >> Vladimir Sacek >> >> >> >> >> _______________________________________________ >> ATM mailing list http://www.atmlist.net/ >> >> >> -------------------------------------------------------------------------------- >> >> >> >> No virus found in this incoming message. >> Checked by AVG - www.avg.com >> Version: 8.0.237 / Virus Database: 270.11.9/1992 - Release >> Date: 03/09/09 19:20:00 > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.0.237 / Virus Database: 270.11.9/1992 - Release Date: 03/09/09 19:20:00 From lm at resulture.com Thu Mar 12 21:24:15 2009 From: lm at resulture.com (lm at resulture.com) Date: Thu, 12 Mar 2009 13:24:15 +0100 Subject: [ATM] grit and pitch suppliers In-Reply-To: References: <017101c9a0b7$78d23070$6a769150$@com> Message-ID: Hello Berthold, (sorry this late answer but my first post bounced) You should look at this url > http://www.stathis-firstlight.de/spiegelschleifen/materialeng.htm Stathis Kafalis in Germany can supply you with the finest borosilicate glass and also grit in almost all sizes. He also has Cerium. Locally you might be able to find shops that polish stones for jewelry and the kind. They use the same SiC grit as we do and you might be able to at least buy the coarser sizes cheap. If you live near the sea you might be able to find pitch in a harbor shop. It is used to make old wooden boats water tight together with wool or other fibers that is soaked with hot pitch and fitted in between the wood planks of the boat. I have no idea what this work is called in English (or Spanish) ?!?!? Med venlig hilsen / Yours faithfully / Mit freundlichen Gr??en Lars Malmgren From: Dominic-Luc Webb To: ATM Superheros Date: 09-03-2009 14:43 Subject: Re: [ATM] grit and pitch suppliers On Mon, 9 Mar 2009, Berthold Hamburger wrote: > Hi, > > > > After many years I am getting back to grinding and would like to know > whether somebody can recommend suppliers for grinding grit and pitch in > Europe and preferably Spain. Larger SiC up to about #600 (average particle ~17 micron) can be had from a number of abrasives suppliers one can find in local phone book. I still get the fine SiC (#600- #1200) and CeO from Microabrasives Corp in MA, USA. They did not take small orders previously, but the past few years I have been ordering boxes of several sizes at a time directly from them. I do not know if Microabrasives sells pitch. My purchases have always worked out, but they have historically ignored email, so I call in my orders when in the States. For the moment, they have been laying off people, so patience needed: http://www.masslive.com/news/index.ssf/2009/02/micro_abrasives_corp_in_westfi.html?category=Business&category=Westfield Some people order from gotgrit.com. Prices at the time I checked were higher than Microabrasives, but Gotgrit has pitch (mirror kits???) that can be ordered at same time. Dominic _______________________________________________ ATM mailing list http://www.atmlist.net/ From richard at foucault.co.uk Thu Mar 12 21:54:50 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Thu, 12 Mar 2009 12:54:50 +0000 Subject: [ATM] grit and pitch suppliers In-Reply-To: References: <017101c9a0b7$78d23070$6a769150$@com> Message-ID: <381199432.20090312125450@foucault.co.uk> Hello lm, Thursday, March 12, 2009, 12:24:15 PM, you wrote: > I have no idea what this work is called in English (or Spanish) ?!?!? Well, they are separate jobs. Stuffing the rope in is Caulking and pitching or tarring after it is filled is called Paying. Very tedious and disliked work. The longest gap to be caulked was called the Devil, hence "There'll be the Devil to pay" and being "between the Devil and the deep blue sea". The original phrase was "The Devil to pay, and no pitch hot" -- Best regards, Richard in the UK (a seafaring nation) From jroyston at gmx.de Fri Mar 13 00:04:34 2009 From: jroyston at gmx.de (Jeremy Royston) Date: Thu, 12 Mar 2009 16:04:34 +0100 Subject: [ATM] grit and pitch suppliers In-Reply-To: References: <017101c9a0b7$78d23070$6a769150$@com> Message-ID: <000c01c9a323$dbe26540$93a72fc0$@de> Hello Lars, This work is called caulking in English (to caulk, pronounced the same as "cork") Ships supplies dealers are also called chandlers Best wishes, Jerry If you live near the sea you might be able to find pitch in a harbor shop. It is used to make old wooden boats water tight together with wool or other fibers that is soaked with hot pitch and fitted in between the wood planks of the boat. I have no idea what this work is called in English (or Spanish) ?!?!? From jroyston at gmx.de Fri Mar 13 00:17:35 2009 From: jroyston at gmx.de (Jeremy Royston) Date: Thu, 12 Mar 2009 16:17:35 +0100 Subject: [ATM] WG: grit and pitch suppliers Message-ID: <000d01c9a325$ac6fdf20$054f9d60$@de> Hello all, I stand corrected by Richard - I'm forgetting my English after almost 40 years in Germany Jerry Hello Lars, This work is called caulking in English (to caulk, pronounced the same as "cork") Ships supplies dealers are also called chandlers From vorblesnak at peak.org Fri Mar 13 06:40:58 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Thu, 12 Mar 2009 14:40:58 -0700 (PDT) Subject: [ATM] Suggestions In-Reply-To: References: Message-ID: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> I will be starting the 48 inch project in the next week. This will be a 48 inch f3 instrument scope. The primary will be glass foam composite with a table top for the mirror surface. The face is 3/8ths thick, the glass foam puck will be 4 inches, perhaps 8 inches if I can score some more foam. This brings us to the suggestion place. Working this blank. Full tool, partial tool, MOT, TOT, by machine, under an assumed name??? David Davis Toledo, OR 97391 From shane at ct-astronomer.com Fri Mar 13 06:46:25 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Thu, 12 Mar 2009 17:46:25 -0400 Subject: [ATM] Suggestions In-Reply-To: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> Message-ID: Hi, Is there somewhere to see the research and techniques on this approach w/ a composite foam/glass mirror? I'm not sure I have the guts in a 48", but I'd at least like to do a little reading on it and see if it's in my grasp. Thanks, Shane LaPierre On Mar 12, 2009, at 5:40 PM, vorblesnak at peak.org wrote: > I will be starting the 48 inch project in the next week. This will > be a 48 > inch f3 instrument scope. The primary will be glass foam composite > with a > table top for the mirror surface. The face is 3/8ths thick, the > glass foam > puck will be 4 inches, perhaps 8 inches if I can score some more foam. > > This brings us to the suggestion place. Working this blank. Full tool, > partial tool, MOT, TOT, by machine, under an assumed name??? > > David Davis > Toledo, OR 97391 > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From gfbrandenburg at yahoo.com Fri Mar 13 10:31:05 2009 From: gfbrandenburg at yahoo.com (Guy Brandenburg) Date: Thu, 12 Mar 2009 18:31:05 -0700 (PDT) Subject: [ATM] WG: grit and pitch suppliers Message-ID: <30537.85316.qm@web111514.mail.gq1.yahoo.com> I pronounce corking and caulking differently, myself. Not that it matters. Guy Brandenburg, Washington, DC My home page on astronomy, mathematics, education: http://home.earthlink.net/~gfbranden/GFB_Home_Page.html or else http://tinyurl.com/r6fh2 ============================= "Education isn't rocket science. It's much, much harder." (Author unknown) --- On Thu, 3/12/09, Jeremy Royston wrote: > From: Jeremy Royston > Subject: [ATM] WG: grit and pitch suppliers > To: atm at atmlist.net > Date: Thursday, March 12, 2009, 11:17 AM > Hello all, > ??? I stand corrected by Richard - I'm > forgetting my English after > almost 40 years in Germany > > Jerry > > Hello Lars, > ???This work is called caulking in English > (to caulk, pronounced the same as > "cork") > Ships supplies dealers are also called chandlers > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From tcohen at blakeglobal.com Fri Mar 13 11:19:50 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Thu, 12 Mar 2009 19:19:50 -0700 Subject: [ATM] Suggestions In-Reply-To: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> Message-ID: I'm pretty sure 3/8-inch front plate is too thin to accommodate a saggitta of this magnitude, even if you were to grind in the parabola on the first attempt. Perhaps it would work if the glass was slumped into shape prior to fine grinding. I started with 3/4-inch table top glass and now have only about 1/4 to 3/8-inch of thickness left to work with at the center - I can't go back to grinding or I'll grind all the way through the center of it. -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of vorblesnak at peak.org Sent: Thursday, March 12, 2009 2:41 PM To: atm at atmlist.net Subject: [ATM] Suggestions I will be starting the 48 inch project in the next week. This will be a 48 inch f3 instrument scope. The primary will be glass foam composite with a table top for the mirror surface. The face is 3/8ths thick, the glass foam puck will be 4 inches, perhaps 8 inches if I can score some more foam. This brings us to the suggestion place. Working this blank. Full tool, partial tool, MOT, TOT, by machine, under an assumed name??? David Davis Toledo, OR 97391 _______________________________________________ ATM mailing list http://www.atmlist.net/ From tcohen at blakeglobal.com Fri Mar 13 11:44:38 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Thu, 12 Mar 2009 19:44:38 -0700 Subject: [ATM] Suggestions In-Reply-To: References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> Message-ID: A 48-inch F3 with any glass thickness is impossible for an amateur. By hand, it would probably take about 10 years to complete just the mirror. Furthermore, the glass and the tool would both be too heavy to lift. The glass would be difficult to mount, and would require a huge engineering job to design the appropriate telescope tube and mounting. After 10 years of work, you might find that the figure on the glass is so bad, that it is only equivalent to the power of a 6-inch mirror. The cost, complexity and difficulty of the project increases exponentially with the size of the mirror. Also, an F/3 parabola is very difficult to figure accurately without expensive equipment. You're better off sticking to what everyone else is doing in the 8"-inch F/6 to F/10 range, which can be achieved relatively quickly and accurately. Ted Cohen Joseph J. Blake and Associates, Inc. One Concord Center 2300 Clayton Road, Suite 1300 Concord, CA 94520 925-356-0950 ext. 112 (phone) 925-356-0956 (fax) tcohen at blakeglobal.com www.blakeglobal.com -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Ted Cohen Sent: Thursday, March 12, 2009 7:20 PM To: atm at atmlist.net Subject: Re: [ATM] Suggestions I'm pretty sure 3/8-inch front plate is too thin to accommodate a saggitta of this magnitude, even if you were to grind in the parabola on the first attempt. Perhaps it would work if the glass was slumped into shape prior to fine grinding. I started with 3/4-inch table top glass and now have only about 1/4 to 3/8-inch of thickness left to work with at the center - I can't go back to grinding or I'll grind all the way through the center of it. -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of vorblesnak at peak.org Sent: Thursday, March 12, 2009 2:41 PM To: atm at atmlist.net Subject: [ATM] Suggestions I will be starting the 48 inch project in the next week. This will be a 48 inch f3 instrument scope. The primary will be glass foam composite with a table top for the mirror surface. The face is 3/8ths thick, the glass foam puck will be 4 inches, perhaps 8 inches if I can score some more foam. This brings us to the suggestion place. Working this blank. Full tool, partial tool, MOT, TOT, by machine, under an assumed name??? David Davis Toledo, OR 97391 _______________________________________________ ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ From deepsky4565 at comcast.net Fri Mar 13 12:02:19 2009 From: deepsky4565 at comcast.net (Daniel Bakken) Date: Thu, 12 Mar 2009 20:02:19 -0700 Subject: [ATM] Suggestions In-Reply-To: References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> Message-ID: <004601c9a388$20a7d700$61f78500$@net> This sounds interesting. How exactly is the foam connected to the faceplate? If you're starting next week, why wouldn't you know the thickness? This would take a while to anneal, unless they aren't melted together. If they aren't, why use glass foam? Another big question is the curve generation. With a 3/8" faceplate, I assume you have slumped it, otherwise this isn't thick enough for your sagitta. Without this information, it seems very premature to start grinding! I certainly wouldn't say it is impossible, since I ground and figured a 41" f3.9 by hand. It was 2" thick pyrex already curve generated. You can check out that process at www.wonderfuluniverse.com. Good luck. Daniel Bakken -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of vorblesnak at peak.org Sent: Thursday, March 12, 2009 2:41 PM To: atm at atmlist.net Subject: [ATM] Suggestions I will be starting the 48 inch project in the next week. This will be a 48 inch f3 instrument scope. The primary will be glass foam composite with a table top for the mirror surface. The face is 3/8ths thick, the glass foam puck will be 4 inches, perhaps 8 inches if I can score some more foam. This brings us to the suggestion place. Working this blank. Full tool, partial tool, MOT, TOT, by machine, under an assumed name??? David Davis Toledo, OR 97391 _______________________________________________ ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ From foreilly at verizon.net Fri Mar 13 12:18:53 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Thu, 12 Mar 2009 23:18:53 -0400 Subject: [ATM] Suggestions References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> Message-ID: <57FCA0B654D040C79FEE12F060E38AD5@HELENYLCMWAV95> David, Th saggitta is computed as r squared/2R 24 squared /144*2 That is 576/288 or Two inches I suspect that such a sag would be difficult unless the glass was slumped. By the way, how is the annealing on the tabletop? Best of luck, Francis J. O'Reilly ----- Original Message ----- From: To: Sent: Thursday, March 12, 2009 5:40 PM Subject: [ATM] Suggestions >I will be starting the 48 inch project in the next week. This will be a 48 > inch f3 instrument scope. The primary will be glass foam composite with a > table top for the mirror surface. The face is 3/8ths thick, the glass foam > puck will be 4 inches, perhaps 8 inches if I can score some more foam. > > This brings us to the suggestion place. Working this blank. Full tool, > partial tool, MOT, TOT, by machine, under an assumed name??? > > David Davis > Toledo, OR 97391 > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From jkoptic at juno.com Fri Mar 13 12:45:19 2009 From: jkoptic at juno.com (Jarvis Krumbein) Date: Thu, 12 Mar 2009 20:45:19 -0700 Subject: [ATM] Suggestions Message-ID: <20090312.204519.2404.0.jkoptic@juno.com> David, I would like to see a smaller mirror (say 12") successfully completed including figuring before starting on such an ambitious project, this just to prove the concept. Have you actually done this? Jarvis Krumbein On Thu, 12 Mar 2009 14:40:58 -0700 (PDT) vorblesnak at peak.org writes: > I will be starting the 48 inch project in the next week. This will be > a 48 > inch f3 instrument scope. The primary will be glass foam composite > with a > table top for the mirror surface. The face is 3/8ths thick, the > glass foam > puck will be 4 inches, perhaps 8 inches if I can score some more > foam. > > This brings us to the suggestion place. Working this blank. Full > tool, > partial tool, MOT, TOT, by machine, under an assumed name??? > > David Davis > Toledo, OR 97391 > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > ____________________________________________________________ Longing for love? Click here for ultimate romantic vacations to Italy. http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTJ67xZf3d1DeAmKSpCwi34sJMoaC7MbFDUhIWbXCPstsl1POP7hgk/ From vorblesnak at peak.org Fri Mar 13 14:55:46 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Thu, 12 Mar 2009 22:55:46 -0700 (PDT) Subject: [ATM] Suggestions Message-ID: <54809.4.242.233.180.1236923746.squirrel@webmail.peak.org> Too much left unsaid, but I thought perhaps you guys had been following the posts. Then I looked and the last post was in February involving the 16 inch glass and foam fused composite and it was pretty terse. So I admit to posting in a vacuum and my apologies. In summary .. The fused blanks have large errors in the curves. This due to the foam distorting as it is heated to fusion temperature. There is no clean way around this, the edge of the foam will distort. If the glass blank is around 70% of the foam diameter, (7 inch glass on a 10 inch foam puck), the curve is true enough to grind. If I could find a water type glass that melted at say 900F to 1000F, I could fuse with out the foam edge failing. Or conversely, if I could find a foam with a melting temperature of 1500F or more I could make it work. So for right now fusing the glass and foam is not a solution. Plan 2, adhesive. I have run an experiment with a slumped disk of glass, 1/8th inch window glass, glued to a glass foam puck using Gorilla Glue. The adhesion was excellent. The glass ground smooth in about 45 minutes with 120 grit. It did not fall off of the foam. I will finish that mirror tomorrow. It is a 12 inch f6. Total thickness is about 2 inches. I have an experiment running right now to answer the question, can I slump two pieces of glass together and keep them separate. I tried 1050F and the glass stayed unstuck but did not slump fully. I am rerunning the test at 1100F with a 1 hour soak. I will have the results tomorrow. If that works, and I think it will, I will slump the 28 inch and 30 inch disks together in the same mold. The 30 will become the mirror and the 28 will be the tool. When they are complete I hope to have a 30 inch f2.5 mirror and a 28 inch f2.5 positive sphere. These are to work up to get ready for the 48. The 48 will go into the kiln on Sunday, I hope, Monday at the latest, with a 42 inch on top for a tool. I will then glue the 48 to a glass foam stack. It will be at least 4 inches thick but I hope to take it to 8 inches thick with the purchase of more foam at some point. I hope to start grinding on the 48 by April 1, (good date eh??), with a completion in early summer. Should be fun. BUT! I would also like to hear some suggestions or ideas for grinding techniques on a big old piece of glass. You may have the next oh ma god technique in your mind and I would like to hear it. I have toyed with the idea of laying the mirror on the floor and grinding the thing tool on top. Then I could just hose it off between wets. For a grinder I thought about a device not unlike a buffer or a floor polisher running very slowly and swept back and forth over the glass as it rotates around the mirror. No I don't know what it looks like, I have not gotten that far. WEIGHT!! The glass top weighs in at around 60 pounds. The glass foam weighs in at 30 something pounds. So the mirror should weigh in at close to 100 pounds. I can hand grind that. But I will post the weight of the blank once I have it put together. I will weight the 12 inch and the 16 inch and the 18 inch and let you know what the weight is on those. David Davis Toledo, OR 97391 >I will be starting the 48 inch project in the next week. This will be a 48 >inch f3 instrument scope. The primary will be glass foam composite with a >table top for the mirror surface. The face is 3/8ths thick, the glass foam >puck will be 4 inches, perhaps 8 inches if I can score some more foam. >This brings us to the suggestion place. Working this blank. Full tool, >partial tool, MOT, TOT, by machine, under an assumed name??? >David Davis >Toledo, OR 97391 From shane at ct-astronomer.com Fri Mar 13 21:43:35 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Fri, 13 Mar 2009 08:43:35 -0400 Subject: [ATM] Suggestions In-Reply-To: <54809.4.242.233.180.1236923746.squirrel@webmail.peak.org> References: <54809.4.242.233.180.1236923746.squirrel@webmail.peak.org> Message-ID: <0B28053F-7213-466E-8308-50E35ABCF2A7@ct-astronomer.com> I would think most people on this list would be very interested in hearing the end-result: the quality and integrity of the final mirror & figure. If that turns out well, then great. What results have you encountered doing a mirror this way? I am unclear how much of the grinding process you have done. I know you mentioned you are working a 12" f6 and will be finished tomorrow... not sure what you mean by finished. It usually takes a while to make a quality 12". Anyway, hope you don't mind commenting back on this. Best wishes, Shane LaPierre On Mar 13, 2009, at 1:55 AM, vorblesnak at peak.org wrote: > Too much left unsaid, but I thought perhaps you guys had been > following > the posts. Then I looked and the last post was in February involving > the > 16 inch glass and foam fused composite and it was pretty terse. So I > admit > to posting in a vacuum and my apologies. In summary .. > > The fused blanks have large errors in the curves. This due to the foam > distorting as it is heated to fusion temperature. There is no clean > way > around this, the edge of the foam will distort. If the glass blank is > around 70% of the foam diameter, (7 inch glass on a 10 inch foam > puck), > the curve is true enough to grind. If I could find a water type > glass that > melted at say 900F to 1000F, I could fuse with out the foam edge > failing. > Or conversely, if I could find a foam with a melting temperature of > 1500F > or more I could make it work. So for right now fusing the glass and > foam > is not a solution. Plan 2, adhesive. > > I have run an experiment with a slumped disk of glass, 1/8th inch > window > glass, glued to a glass foam puck using Gorilla Glue. The adhesion was > excellent. The glass ground smooth in about 45 minutes with 120 > grit. It > did not fall off of the foam. I will finish that mirror tomorrow. It > is a > 12 inch f6. Total thickness is about 2 inches. > > I have an experiment running right now to answer the question, can I > slump > two pieces of glass together and keep them separate. I tried 1050F > and the > glass stayed unstuck but did not slump fully. I am rerunning the > test at > 1100F with a 1 hour soak. I will have the results tomorrow. If that > works, > and I think it will, I will slump the 28 inch and 30 inch disks > together > in the same mold. The 30 will become the mirror and the 28 will be the > tool. When they are complete I hope to have a 30 inch f2.5 mirror > and a 28 > inch f2.5 positive sphere. These are to work up to get ready for the > 48. > > The 48 will go into the kiln on Sunday, I hope, Monday at the > latest, with > a 42 inch on top for a tool. I will then glue the 48 to a glass foam > stack. It will be at least 4 inches thick but I hope to take it to 8 > inches thick with the purchase of more foam at some point. I hope to > start > grinding on the 48 by April 1, (good date eh??), with a completion in > early summer. Should be fun. BUT! I would also like to hear some > suggestions or ideas for grinding techniques on a big old piece of > glass. > You may have the next oh ma god technique in your mind and I would > like to > hear it. > > I have toyed with the idea of laying the mirror on the floor and > grinding > the thing tool on top. Then I could just hose it off between wets. > For a > grinder I thought about a device not unlike a buffer or a floor > polisher > running very slowly and swept back and forth over the glass as it > rotates > around the mirror. No I don't know what it looks like, I have not > gotten > that far. > > WEIGHT!! The glass top weighs in at around 60 pounds. The glass foam > weighs in at 30 something pounds. So the mirror should weigh in at > close > to 100 pounds. I can hand grind that. But I will post the weight of > the > blank once I have it put together. I will weight the 12 inch and the > 16 > inch and the 18 inch and let you know what the weight is on those. > > David Davis > Toledo, OR 97391 > >> I will be starting the 48 inch project in the next week. This will >> be a 48 >> inch f3 instrument scope. The primary will be glass foam composite >> with a >> table top for the mirror surface. The face is 3/8ths thick, the >> glass foam >> puck will be 4 inches, perhaps 8 inches if I can score some more >> foam. > > >> This brings us to the suggestion place. Working this blank. Full >> tool, >> partial tool, MOT, TOT, by machine, under an assumed name??? > > >> David Davis >> Toledo, OR 97391 > > > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From camkit at mweb.co.za Sat Mar 14 00:57:33 2009 From: camkit at mweb.co.za (chris forder) Date: Fri, 13 Mar 2009 17:57:33 +0200 Subject: [ATM] grit and pitch suppliers In-Reply-To: References: Message-ID: <49BA826D.8020308@mweb.co.za> Hi, The process of sealing (watertighting) wodden planked boats with pitch and a form of rope is called "Caulking" - pronounced corking. Chris Cape Town From masutokw at yahoo.es Sat Mar 14 03:48:10 2009 From: masutokw at yahoo.es (=?iso-8859-1?Q?=C1ngel_Caparr=F3s?=) Date: Fri, 13 Mar 2009 18:48:10 +0000 (GMT) Subject: [ATM] grit and pitch suppliers References: <017101c9a0b7$78d23070$6a769150$@com> <000c01c9a323$dbe26540$93a72fc0$@de> Message-ID: <485522.1648.qm@web26902.mail.ukl.yahoo.com> In spanish "calafatear" From andalusian arabian "galafat" = carpenter, boat builder, ________________________________ De: Jeremy Royston Para: lm at resulture.com CC: atm at atmlist.net Enviado: jueves, 12 de marzo, 2009 16:04:34 Asunto: Re: [ATM] grit and pitch suppliers Hello Lars, This work is called caulking in English (to caulk, pronounced the same as "cork") Ships supplies dealers are also called chandlers Best wishes, Jerry If you live near the sea you might be able to find pitch in a harbor shop. It is used to make old wooden boats water tight together with wool or other fibers that is soaked with hot pitch and fitted in between the wood planks of the boat. I have no idea what this work is called in English (or Spanish) ?!?!? _______________________________________________ ATM mailing list http://www.atmlist.net/ From funnybone101 at embarqmail.com Sat Mar 14 04:57:07 2009 From: funnybone101 at embarqmail.com (Mitchell Revalski) Date: Fri, 13 Mar 2009 15:57:07 -0400 Subject: [ATM] Suggestions In-Reply-To: References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> Message-ID: <4B201BFED81542BDB3B1B10D54ECF60D@dmp> I must agree, but then again... There is never the chance for success unless there is an equal chance for failure. If no one pushed the envelope think of how boring things would be. ""It is no sin to try and fail, the only sin is not to make the attempt"" :) Mitch -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Ted Cohen Sent: Thursday, March 12, 2009 10:45 PM To: atm at atmlist.net Subject: Re: [ATM] Suggestions A 48-inch F3 with any glass thickness is impossible for an amateur. By hand, it would probably take about 10 years to complete just the mirror. Furthermore, the glass and the tool would both be too heavy to lift. The glass would be difficult to mount, and would require a huge engineering job to design the appropriate telescope tube and mounting. After 10 years of work, you might find that the figure on the glass is so bad, that it is only equivalent to the power of a 6-inch mirror. The cost, complexity and difficulty of the project increases exponentially with the size of the mirror. Also, an F/3 parabola is very difficult to figure accurately without expensive equipment. You're better off sticking to what everyone else is doing in the 8"-inch F/6 to F/10 range, which can be achieved relatively quickly and accurately. Ted Cohen Joseph J. Blake and Associates, Inc. One Concord Center 2300 Clayton Road, Suite 1300 Concord, CA 94520 925-356-0950 ext. 112 (phone) 925-356-0956 (fax) tcohen at blakeglobal.com www.blakeglobal.com -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Ted Cohen Sent: Thursday, March 12, 2009 7:20 PM To: atm at atmlist.net Subject: Re: [ATM] Suggestions I'm pretty sure 3/8-inch front plate is too thin to accommodate a saggitta of this magnitude, even if you were to grind in the parabola on the first attempt. Perhaps it would work if the glass was slumped into shape prior to fine grinding. I started with 3/4-inch table top glass and now have only about 1/4 to 3/8-inch of thickness left to work with at the center - I can't go back to grinding or I'll grind all the way through the center of it. -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of vorblesnak at peak.org Sent: Thursday, March 12, 2009 2:41 PM To: atm at atmlist.net Subject: [ATM] Suggestions I will be starting the 48 inch project in the next week. This will be a 48 inch f3 instrument scope. The primary will be glass foam composite with a table top for the mirror surface. The face is 3/8ths thick, the glass foam puck will be 4 inches, perhaps 8 inches if I can score some more foam. This brings us to the suggestion place. Working this blank. Full tool, partial tool, MOT, TOT, by machine, under an assumed name??? David Davis Toledo, OR 97391 _______________________________________________ ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ From rozer at pacbell.net Sat Mar 14 05:05:18 2009 From: rozer at pacbell.net (Richard Ozer) Date: Fri, 13 Mar 2009 13:05:18 -0700 Subject: [ATM] Suggestions In-Reply-To: <4B201BFED81542BDB3B1B10D54ECF60D@dmp> References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> <4B201BFED81542BDB3B1B10D54ECF60D@dmp> Message-ID: <49BABC7E.9070106@pacbell.net> Group 70 did it (with full thickness glass however). http://en.wikipedia.org/wiki/Group_70 It took them about 12 years. Apparently the last three inches were the worst ;-) The important thing is that no-one died in the process. RO Mitchell Revalski wrote: > I must agree, but then again... There is never the chance for success unless > there is an equal chance for failure. If no one pushed the envelope think of > how boring things would be. ""It is no sin to try and fail, the only sin is > not to make the attempt"" :) > > Mitch > > -----Original Message----- > From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of > Ted Cohen > Sent: Thursday, March 12, 2009 10:45 PM > To: atm at atmlist.net > Subject: Re: [ATM] Suggestions > > A 48-inch F3 with any glass thickness is impossible for an amateur. By hand, > it would probably take about 10 years to complete just the mirror. > Furthermore, the glass and the tool would both be too heavy to lift. The > glass would be difficult to mount, and would require a huge engineering job > to design the appropriate telescope tube and mounting. After 10 years of > work, you might find that the figure on the glass is so bad, that it is only > equivalent to the power of a 6-inch mirror. The cost, complexity and > difficulty of the project increases exponentially with the size of the > mirror. Also, an F/3 parabola is very difficult to figure accurately > without expensive equipment. You're better off sticking to what everyone > else is doing in the 8"-inch F/6 to F/10 range, which can be achieved > relatively quickly and accurately. > > > > Ted Cohen > Joseph J. Blake and Associates, Inc. > One Concord Center > 2300 Clayton Road, Suite 1300 > Concord, CA 94520 > 925-356-0950 ext. 112 (phone) > 925-356-0956 (fax) > tcohen at blakeglobal.com > www.blakeglobal.com > > > -----Original Message----- > From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of > Ted Cohen > Sent: Thursday, March 12, 2009 7:20 PM > To: atm at atmlist.net > Subject: Re: [ATM] Suggestions > > I'm pretty sure 3/8-inch front plate is too thin to accommodate a saggitta > of this magnitude, even if you were to grind in the parabola on the first > attempt. Perhaps it would work if the glass was slumped into shape prior to > fine grinding. I started with 3/4-inch table top glass and now have only > about 1/4 to 3/8-inch of thickness left to work with at the center - I can't > go back to grinding or I'll grind all the way through the center of it. > > -----Original Message----- > From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of > vorblesnak at peak.org > Sent: Thursday, March 12, 2009 2:41 PM > To: atm at atmlist.net > Subject: [ATM] Suggestions > > I will be starting the 48 inch project in the next week. This will be a 48 > inch f3 instrument scope. The primary will be glass foam composite with a > table top for the mirror surface. The face is 3/8ths thick, the glass foam > puck will be 4 inches, perhaps 8 inches if I can score some more foam. > > This brings us to the suggestion place. Working this blank. Full tool, > partial tool, MOT, TOT, by machine, under an assumed name??? > > David Davis > Toledo, OR 97391 > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > From arjan.te.marvelde at hetnet.nl Sat Mar 14 05:32:10 2009 From: arjan.te.marvelde at hetnet.nl (Arjan te Marvelde (hetnet)) Date: Fri, 13 Mar 2009 21:32:10 +0100 Subject: [ATM] what to do best? In-Reply-To: References: Message-ID: <49BAC2CA.40609@hetnet.nl> Jan, You could try a few short sessions accentuated pressure with the tool edge just inside outer zone, blending it with adjacent zones esp. toward center. Measure whether things move the right way. You may end up with a rough surface though. Arjan > I parabolizing my 204 mm f/3.85. Edge correction is to much. What is the > best way to reduce the edge correction? > > See http://members.ziggo.nl/jhm.vangastel/Astronomy/xp.htm > From wa4guu at verizon.net Sat Mar 14 07:35:36 2009 From: wa4guu at verizon.net (Jerry) Date: Fri, 13 Mar 2009 18:35:36 -0400 Subject: [ATM] what to do best? In-Reply-To: <2C0EA6F9809F4D5486411811AD73B2F5@niks03981037eb> Message-ID: <5675731591ED4891814D4F5A216791BE@D85SJB21> -----Original Message----- From: Jan van Gastel Subject: [ATM] what to do best? I parabolizing my 204 mm f/3.85. Edge correction is to much. What is the best way to reduce the edge correction? **************************************** Hello Jan, A Ronchi test might help decide. Depending on the way the Ronchi bands look in the edge zones makes a difference in what might be the best. Let's say you have the grating inside ROC and about 6 bands showing on the mirror, 3 on each side of center. Look at the two closest to center and look at the top of the mirror (so we are on the same page). They could look some thing like this ( ) | | (picture the bars having a more normal curve and then hooking through the last zone and off the edge at the top.) Meaning the over-correction continues through the zone. Or they might look something like this || ( ) Meaning that the most of the over correction is a little ways inward from the edge, maybe in zone 5 and that zone 6 is could still be somewhat spherical. If this is the case some of the over-correction can be spread into zone 6 while reducing the over-correction. AND NOW CONCERNING YOUR PREVIOUS-----Original Message----- From: Jan van Gastel Subject: [ATM] first measurements I use a moving source Foucault tester. Last readings (in millimeters) are: 0.00, 0.41, 0.66, 1.11, 1.57, 2.01, so zone 3 is lagging behind. Think I will use a narrower W in zone 3 now, do also a bit more work at the center in the next session and make my session 10 minutes. From: Jan van Gastel Subject: [ATM] first measurements I use a moving source Foucault tester. Last readings (in millimeters) are: 0.00, 0.41, 0.66, 1.11, 1.57, 2.01, so zone 3 is lagging behind. Think I will use a narrower W in zone 3 now, do also a bit more work at the center in the next session and make my session 10 minutes. ---------END OF JAN'S MESSAGE ----------------- Ok Jan, here is your data as you have provide before and after. Previous test percentages of correction for each zone are on left and last test percentages on the right. I don't know how many sessions you did in between. Zone 1 > 80% 67% Zone 2 > 50% 69% Zone 3 > 89% 52% Zone 4 > 91% 127% Zone 5 > 88% 237% Zone 6 I like to put it that way so that it is clear that the percentage is from one zone to the next. Typical figuring usually means that working zone 5 will reduce the correction from zones 4 to 5 as correction is increase from 5 to 6. That is because working zone 5 usually means making its ROC shorter. That would move it closer to the ROC of 4 and farther from the ROC of 6. It looks like you actually ended up working zones 2, 4 and 5 more than zone 3. I look at your results this way: You shortened the ROC of zone 2 making it closer to the ROC of zone 1 changing the percentage from 80% to 67%. Shortening the ROC of zone 2 also made it farther from the ROC of zone 3 making the percentage there go up from 50% to 69%. Apparently zone 4 got some work making its ROC shorter and closer to the ROC of zone 3 making the correction from 3 to 4 go down from 89% to 52%. And the ROC of zone 4 having been made shorter is now farther from zone 5 increasing correction from 91% to 127%. Apparently zone 5 got some work along with 4 ratcheting up the correction from 5 to 6. It could have been that you did something that rolled the outer zones to a turn down. I recommend only working one zone at a time so that you can see exactly what happens compared to what you think will happen when you work a particular zone. Wait until you have gained much experience before fixing multiple problems in one session. I would be tempted to do about 5 minutes of TOT W stroke to see if I could take that raised zone at 92% down. Alternatively is Texereau's Fig. 42 examples 6 (top) and 7 (which is also for 6 (bottom). I would decide which by how the Ronchi bands look as explained above. Concerning examples 6 and 7, the same effect can be had working MOT by applying pressure on the other hand. Black hand TOT. White hand MOT You can visualize Fig. 42 example 7 as working "zone 8" so that correction goes down inward. Inward in this case is from the edge. This can push the peak inward. Wouldn't you like that. Almost anything you do will make that look more like a turned down edge. The peak at 92 % will probably move closer to the edge as you push it down. You can treat it like a TDE and push the peak off the edge. Don't do anything out at the edge too long before looking at the result. Sometimes when working one "ugly" out you might pass through perfection to another "ugly". One or two trips around can sometimes be enough to see dramatic results at the edge, either good or bad. Good luck... Jerry From russjocoy at hotmail.com Sat Mar 14 09:41:52 2009 From: russjocoy at hotmail.com (Russell Jocoy) Date: Fri, 13 Mar 2009 20:41:52 -0400 Subject: [ATM] David Davis.. 48 " disk with Glass foam backing Message-ID: David, I and Andrew A. have discussed this application. It seems that the fusion of the suface glass and the glass foam substrate is very stable. The problem comes when you strat to grind and polish. Even though the surface glass is slumped to a curve that is very close to where you need to be. There must be some grinding and polishing going on... Our first problem was side support of the foam substrate on a grinding machine?? This stuff is not really very hard.. Second problem was thickness of the surface glass. Yes it is slumped to a certain F number but grinding and polishing will dig.. I think you had that problem with a 1/4" surface glass. David this is an excellent experiment, but as I and Andrew A. discussed small proto's must be completed to the final figure in order to get to the bigger experiment. If you are going 48 inch with the glass foam back, I would not go less than 3/4" surface glass, that is with a very acurate slump of your choice. Then you will have to deal with the mechanic's of a grinding or polishing machine and the twisting force involved, and whether the surface glass will "rip" or separate during the twisting process.. The glass foam is amazing but you can break it with your hand... RUSS JOCOY _________________________________________________________________ Hotmail? is up to 70% faster. Now good news travels really fast. http://windowslive.com/online/hotmail?ocid=TXT_TAGLM_WL_HM_70faster_032009 From jhm.vangastel at ziggo.nl Sat Mar 14 15:14:38 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Sat, 14 Mar 2009 07:14:38 +0100 Subject: [ATM] what to do best? References: <49BAC2CA.40609@hetnet.nl> Message-ID: <3B091A48D76E4452ADEF3759C311CCB5@niks03981037eb> Arjan, I am not good at the accented pressure method. I have decided to go with Mike Lockwood's idea and went back to a sphere to start again. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Arjan te Marvelde (hetnet)" To: ; "Jan van Gastel" Sent: Friday, March 13, 2009 21:32 Subject: Re: [ATM] what to do best? > Jan, > > You could try a few short sessions accentuated pressure with the tool edge > just inside outer zone, blending it with adjacent zones esp. toward > center. Measure whether things move the right way. You may end up with a > rough surface though. > > Arjan >> I parabolizing my 204 mm f/3.85. Edge correction is to much. What is the >> best way to reduce the edge correction? >> >> See http://members.ziggo.nl/jhm.vangastel/Astronomy/xp.htm >> From wa4guu at verizon.net Sun Mar 15 01:45:12 2009 From: wa4guu at verizon.net (Jerry) Date: Sat, 14 Mar 2009 12:45:12 -0400 Subject: [ATM] what to do best? In-Reply-To: <5675731591ED4891814D4F5A216791BE@D85SJB21> Message-ID: <110DC242B00841EB8B78EFC43D3D8119@D85SJB21> Of course I mean that if you are trying to correct particular zones to work one at a time. Nothing wrong with something like variation of the normal W parabolizing strokes to work the entire mirror toward a parabola while concentrating more work in a lagging zone so that it will catch up to the rest of the mirror. As Arjan suggests, too much correction of individual zones can make the mirror rough, or make the zones like steps across the mirror. There are ways to reap the benefit while avoiding the problems. Like everything else, it probably won't come naturally, but will have to be learned. -----Original Message----- From: Jerry I recommend only working one zone at a time so that you can see exactly what happens compared to what you think will happen when you work a particular zone. Wait until you have gained much experience before fixing multiple problems in one session. From mbartels at bbastrodesigns.com Sun Mar 15 02:35:32 2009 From: mbartels at bbastrodesigns.com (Mel Bartels) Date: Sat, 14 Mar 2009 10:35:32 -0700 Subject: [ATM] what to do best? In-Reply-To: <3B091A48D76E4452ADEF3759C311CCB5@niks03981037eb> References: <49BAC2CA.40609@hetnet.nl> <3B091A48D76E4452ADEF3759C311CCB5@niks03981037eb> Message-ID: <005001c9a4cb$4ad8d350$e08a79f0$@com> >>> I am not good at the accented pressure method. I have decided to go with Mike Lockwood's idea and went back to a sphere to start again. <<< Overcorrected edge zones can be difficult. Here's what I do in lieu of spending all that time returning to sphere. I alter my lap ala the deformed or area lap concept. This idea goes back to the earliest days of optical making. I scratch a very thin layer (it can be pressed away with waxed paper) of pitch in the middle of the lap, say out to the 60% zone. Strokes are very short, no side swing, mirror on top. I find that I can return to a sphere in 20 minutes to 2 hrs depending on the circumstance. About that time, the central zones will be coming back into contact. Mel Bartels From dlwebb at canit.se Sun Mar 15 02:37:34 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Sat, 14 Mar 2009 18:37:34 +0100 (MET) Subject: [ATM] Maksutov-Cassegrain: Curvature of field Message-ID: Regards applying curvature of field equation in "classical" Cass design to a Mak-Cass: 1/Rf = -(2/R1 - 2/R2) where, Rf = curvature of focused image surface (i.e., field); R1 and R2 = radii of curvature for primary and secondary mirror, resp. Starting from a prime focus system without secondary, adding the meniscus changes effective focal length, so does this not change effective radius of curvature such that I should apply an effective primary radius of curvature (effR1)? Any thoughts on a curvature of field calculation for a Mak-Cass, like: 1/Rf = -(2/effR1 - 2/R2) This is design reasoning where I start with a Mak camera at prime focus, then add Cass secondary. Can/does Oslo have ability to solve this? I have problems determining what the correct Rf should be given the rest of design is clamped. Along similar lines, anyone know what is meant in Oslo with an image surface thickness with a value like, say 22 mm, obtained by setting this as variable and running optimization iterations? Dominic From wa4guu at verizon.net Sun Mar 15 03:32:38 2009 From: wa4guu at verizon.net (Jerry) Date: Sat, 14 Mar 2009 14:32:38 -0400 Subject: [ATM] what to do best? In-Reply-To: <2C0EA6F9809F4D5486411811AD73B2F5@niks03981037eb> Message-ID: Jan Here is a "trick" worth knowing. Looking at the profile at the link in your message below... The first two zones are at close to 67% correction. The hill in the center represents a 67% corrected profile. Continue the slope of that on down and out to the edge. You should see that even with the over-corrected outer zones, the edge is still quite high compared to the 67% corrected center. That means you had plenty of room to push the peak at 92% over the edge without resulting in a hyperbola (over-corrected). TOT stroke just like normal MOT parabolizing long and wide "W" stroke would have taken that thing down without risk of making the mirror hyperbolic... unless you did it too long. 5 or 10 minutes would have shown you if it would work. Next time.... Jerry -----Original Message----- From: Jan van Gastel Sent: Wednesday, March 11, 2009 8:23 AM To: atm at atmlist.net Subject: [ATM] what to do best? I parabolizing my 204 mm f/3.85. Edge correction is to much. What is the best way to reduce the edge correction? See http://members.ziggo.nl/jhm.vangastel/Astronomy/xp.htm Jan From rflrs at rcn.com Sun Mar 15 06:28:40 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Sat, 14 Mar 2009 16:28:40 -0500 Subject: [ATM] Maksutov-Cassegrain: Curvature of field In-Reply-To: References: Message-ID: <49BC2188.7020303@rcn.com> Dominic-Luc Webb wrote: > Starting from a prime focus system without secondary, > adding the meniscus changes effective focal length, so > does this not change effective radius of curvature such > that I should apply an effective primary radius of > curvature (effR1)? Any thoughts on a curvature of field > calculation for a Mak-Cass, like: > > 1/Rf = -(2/effR1 - 2/R2) > > This is design reasoning where I start with a Mak > camera at prime focus, then add Cass secondary. > Nominally, isn't Rm2 = Rm1 + ((n^2-1)/(n^2))*tm (from R&vV, Ch. 11.3)? Then, approximately, 1/Rm2 = (1/Rm1)*(1-(n^2-1)/(n^2))*tm/Rm1) (note sign change from the truncated series expansion). Wouldn't the first part of the Rf sum above would then be 2/R1 - (n-1)(n^2-1)/(n^3)*t/(Rm1^2) instead of just 1/R1 (assuming my signs are correct here). From vla at copper.net Sun Mar 15 08:12:51 2009 From: vla at copper.net (vladimir sacek) Date: Sat, 14 Mar 2009 19:12:51 -0400 Subject: [ATM] Maksutov-Cassegrain: Curvature of field References: Message-ID: <001001c9a4fa$675e6ab0$3758f804@Handsome> Dominic-Luc Webb wrote: >Any thoughts on a curvature of field >calculation for a Mak-Cass, like: >1/Rf = -(2/effR1 - 2/R2) The effect of meniscus on the system Petzval is negligible. Its astigmatism contribution can have more effect on the (actual) best surface curvature. It is more complicated than just mirrors' Petzval: you need to take into account stop position, as well as astigmatic contributions of all three optical elements. You may find my ramblings helpful: http://www.telescope-optics.net/MCT_off_axis.htm Vla From jack.swaton at starryhost.com Sun Mar 15 14:06:02 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Sat, 14 Mar 2009 22:06:02 -0700 Subject: [ATM] Preference on RFT Message-ID: Does anybody have a preference on scopes for a given 6" aperture? Let's say I had a $1,000 (which unfortunately I don't) to spend on a Mak Newt or a 150mm refractor (this would obviously be a Meade/Celestron/etc). 1) Which would have better contrast, 2) Which would have pin-pointier stars 3) Which would have better light throughput? 4) Can a minus violet filter make the refractor more apo-like? ' Let's say they were both short focal lengths: 1) Would one respond better to barlows for better planetary visual observing? Let's say they were both long focal lengths.would one be better as an RFT scope? The reason why I'm asking is that as I grow older in my observing, my tastes changes. 13 inch scopes become too unwieldy and inexpensive refractors unacceptable with a heavy Denk bino or my family requires ultrafast observing sessions or. So I'm looking to acquire optics to build a small scope and have not had the opportunity to look through different scopes in several years. I want the perfect scope for that lovely RFT experience with black sky and pinpoint stars but that can also wow folks with the moon and planets. In short, I want the perfect scope. :-) If I go refractor, I'll probably build a bent light path so I can control the eyepiece elevation. If I go Mak Newt (or other design). I'll have to punt and learn what I can do with those. Thanks, Jack Swaton Starry Host From astroguy at nas.com Sun Mar 15 14:40:57 2009 From: astroguy at nas.com (astroguy at nas.com) Date: Sun, 15 Mar 2009 01:40:57 -0400 Subject: [ATM] Preference on RFT Message-ID: <380-22009301554057924@M2W019.mail2web.com> I absolutely love my my 5" f/10 D&G refractor. It is simply, wonderful, fantastic, incredible, super, duper, great, the BEST!! Purrrrfect for planets!!! I absolutely love my my 6" f/5 Mak/Newt. It is simply, wonderful, fantastic, incredible, super, duper, great, the BEST!! Purrrrfect as an RFT!!! So, now you have your answer, the perfect scope..........s!! And one more thought. Several years ago, was observing at RTMC with Roland Christen of AstroPhysics fame. We used his 6" scope to chase down Pluto. Not only did we find Pluto but we could look directly at the "planet" and see a solid image. Pluto is much more evasive in most scopes. Conclusion: Refractor, Mak/Newt ...................... YES. Kreig Original Message: ----------------- From: Jack Swaton @ Starry Host jack.swaton at starryhost.com Date: Sat, 14 Mar 2009 22:06:02 -0700 To: atm at atmlist.net Subject: [ATM] Preference on RFT Does anybody have a preference on scopes for a given 6" aperture? Let's say I had a $1,000 (which unfortunately I don't) to spend on a Mak Newt or a 150mm refractor (this would obviously be a Meade/Celestron/etc). 1) Which would have better contrast, 2) Which would have pin-pointier stars 3) Which would have better light throughput? 4) Can a minus violet filter make the refractor more apo-like? ' Let's say they were both short focal lengths: 1) Would one respond better to barlows for better planetary visual observing? Let's say they were both long focal lengths.would one be better as an RFT scope? The reason why I'm asking is that as I grow older in my observing, my tastes changes. 13 inch scopes become too unwieldy and inexpensive refractors unacceptable with a heavy Denk bino or my family requires ultrafast observing sessions or. So I'm looking to acquire optics to build a small scope and have not had the opportunity to look through different scopes in several years. I want the perfect scope for that lovely RFT experience with black sky and pinpoint stars but that can also wow folks with the moon and planets. In short, I want the perfect scope. :-) If I go refractor, I'll probably build a bent light path so I can control the eyepiece elevation. If I go Mak Newt (or other design). I'll have to punt and learn what I can do with those. Thanks, Jack Swaton Starry Host _______________________________________________ ATM mailing list http://www.atmlist.net/ -------------------------------------------------------------------- mail2web.com ? What can On Demand Business Solutions do for you? http://link.mail2web.com/Business/SharePoint From foreilly at verizon.net Mon Mar 16 01:52:31 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Sun, 15 Mar 2009 12:52:31 -0400 Subject: [ATM] Remelting glass Message-ID: <1EA9350702E14702A89DC34D4813A94F@HELENYLCMWAV95> I have a 12.25 inch old blank of questionable parentage that I got I don't remember when from I don't remember where. I believe that it is old pyrex. One side is fine, there are internal cracks on the other side. I intend to make a 12.25 inch flat for use in a small autocollimator. I would like to remelt and anneal the blank before I start in on the flat. I am finishing a number of projects now so I have some time. Does anyone know who might be able to remelt and anneal the glass. The flat will be my opus magnus when done (At least until my next project) I would like to have the internal issues cleared. That being said, I am aware that the internal cracks will not have much impact on the flat whatsoever. I just want them fixed and the annealing to be done to modern standards. Francis J. O'Reilly From jhm.vangastel at ziggo.nl Mon Mar 16 03:28:14 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Sun, 15 Mar 2009 19:28:14 +0100 Subject: [ATM] what to do best? References: <49BAC2CA.40609@hetnet.nl> <3B091A48D76E4452ADEF3759C311CCB5@niks03981037eb> <005001c9a4cb$4ad8d350$e08a79f0$@com> Message-ID: Mel, If I un derstand you well, going back to spherical that way, you decorrect the edge zones first and the center zones will decorrect later, when they have contact again? Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Mel Bartels" To: Sent: Saturday, March 14, 2009 18:35 Subject: Re: [ATM] what to do best? >>>> > I am not good at the accented pressure method. I have decided to go with > Mike Lockwood's idea and went back to a sphere to start again. > <<< > > > Overcorrected edge zones can be difficult. Here's what I do in lieu of > spending all that time returning to sphere. I alter my lap ala the > deformed > or area lap concept. This idea goes back to the earliest days of optical > making. I scratch a very thin layer (it can be pressed away with waxed > paper) of pitch in the middle of the lap, say out to the 60% zone. > Strokes > are very short, no side swing, mirror on top. I find that I can return to > a > sphere in 20 minutes to 2 hrs depending on the circumstance. About that > time, the central zones will be coming back into contact. > > Mel Bartels > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From mbartels at bbastrodesigns.com Mon Mar 16 04:14:01 2009 From: mbartels at bbastrodesigns.com (Mel Bartels) Date: Sun, 15 Mar 2009 12:14:01 -0700 Subject: [ATM] what to do best? In-Reply-To: References: <49BAC2CA.40609@hetnet.nl> <3B091A48D76E4452ADEF3759C311CCB5@niks03981037eb> <005001c9a4cb$4ad8d350$e08a79f0$@com> Message-ID: <005101c9a5a2$44bf1bf0$ce3d53d0$@com> >>> If I understand you well, going back to spherical that way, you decorrect the edge zones first and the center zones will decorrect later, when they have contact again? <<< On a coarse level, yes. On a finer level, I'm talking about increasing the Radius of Curvature of the outer zones and decreasing the difference in the RoC between the individual outer zones. By avoiding polishing action in the center combined with flattening the edge zones to a longer RoC, one can remove the overcorrection quickly. I don't go back to a sphere myself. As soon as the edge zones are brought back down to full parabolization or a bit less, I resume figuring. Mel Bartels From vorblesnak at peak.org Mon Mar 16 06:08:08 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Sun, 15 Mar 2009 14:08:08 -0700 (PDT) Subject: [ATM] Remelting old glass In-Reply-To: References: Message-ID: <2616.69.59.200.230.1237151288.squirrel@webmail.peak.org> Keep in mind that pyrex / borosilicate is notorious for devitrification. Heating and annealing the glass will probably fog the surface of the glass. Grinding will remove it but it is a matter of heat and time. The higher the heat and the longer the soak time the greater the devit. David Davis Toledo, OR 97391 > > Message: 17 > Date: Sun, 15 Mar 2009 12:52:31 -0400 > From: "Francis J. O'Reilly" > Subject: [ATM] Remelting glass > To: > Message-ID: <1EA9350702E14702A89DC34D4813A94F at HELENYLCMWAV95> > Content-Type: text/plain; charset="iso-8859-1" > > I have a 12.25 inch old blank of questionable parentage that I got I don't > remember when from I don't remember where. I believe that it is old pyrex. > > One side is fine, there are internal cracks on the other side. I intend to > make a 12.25 inch flat for use in a small autocollimator. > > I would like to remelt and anneal the blank before I start in on the flat. > I am finishing a number of projects now so I have some time. > > Does anyone know who might be able to remelt and anneal the glass. The > flat will be my opus magnus when done (At least until my next project) I > would like to have the internal issues cleared. > > That being said, I am aware that the internal cracks will not have much > impact on the flat whatsoever. I just want them fixed and the annealing to > be done to modern standards. > > Francis J. O'Reilly > > ------------------------------ > > Message: 18 > Date: Sun, 15 Mar 2009 19:28:14 +0100 > From: "Jan van Gastel" > Subject: Re: [ATM] what to do best? > To: > Message-ID: > Content-Type: text/plain; format=flowed; charset="iso-8859-1"; > reply-type=original > > Mel, > > If I un derstand you well, going back to spherical that way, you decorrect > the edge zones first and the center zones will decorrect later, when they > have contact again? > > Jan > http://members.ziggo.nl/jhm.vangastel/Astronomy/ > > > > ----- Original Message ----- > From: "Mel Bartels" > To: > Sent: Saturday, March 14, 2009 18:35 > Subject: Re: [ATM] what to do best? > > >>>>> >> I am not good at the accented pressure method. I have decided to go >> with >> Mike Lockwood's idea and went back to a sphere to start again. >> <<< >> >> >> Overcorrected edge zones can be difficult. Here's what I do in lieu of >> spending all that time returning to sphere. I alter my lap ala the >> deformed >> or area lap concept. This idea goes back to the earliest days of >> optical >> making. I scratch a very thin layer (it can be pressed away with waxed >> paper) of pitch in the middle of the lap, say out to the 60% zone. >> Strokes >> are very short, no side swing, mirror on top. I find that I can return >> to >> a >> sphere in 20 minutes to 2 hrs depending on the circumstance. About that >> time, the central zones will be coming back into contact. >> >> Mel Bartels >> >> >> >> _______________________________________________ >> ATM mailing list http://www.atmlist.net/ > > > > ------------------------------ > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > End of ATM Digest, Vol 63, Issue 10 > *********************************** > From lenses at roadrunner.com Mon Mar 16 07:10:54 2009 From: lenses at roadrunner.com (lenses at roadrunner.com) Date: Sun, 15 Mar 2009 18:10:54 -0400 Subject: [ATM] Remelting old glass In-Reply-To: <2616.69.59.200.230.1237151288.squirrel@webmail.peak.org> Message-ID: <20090315221054.2SU74.250479.root@cdptpa-web08-z01> Francis, Ask United Lens how much they would charge to do this for you. I would guess that it would be less expensive to just buy a new blank from them. Let us know, I would be curious to see if they would even take on a job like that. My guess is $50.00 but then I am old and give stuff away for free :) Pete From: "Francis J. O'Reilly" I have a 12.25 inch old blank of questionable parentage that I got I don't remember when from I don't remember where. I believe that it is old pyrex. One side is fine, there are internal cracks on the other side. I intend to make a 12.25 inch flat for use in a small autocollimator. I would like to remelt and anneal the blank before I start in on the flat. I am finishing a number of projects now so I have some time. Does anyone know who might be able to remelt and anneal the glass. The flat will be my opus magnus when done (At least until my next project) I would like to have the internal issues cleared. That being said, I am aware that the internal cracks will not have much impact on the flat whatsoever. I just want them fixed and the annealing to be done to modern standards. Francis J. O'Reilly From thomas at moiler.com Mon Mar 16 09:13:17 2009 From: thomas at moiler.com (Thomas Janstrom) Date: Mon, 16 Mar 2009 10:13:17 +1000 Subject: [ATM] Remelting glass In-Reply-To: <1EA9350702E14702A89DC34D4813A94F@HELENYLCMWAV95> References: <1EA9350702E14702A89DC34D4813A94F@HELENYLCMWAV95> Message-ID: <01c601c9a5cc$05415950$0fc40bf0$@com> Francis, Yes it can be done, you would need to get it up to ~1700'F to 1900'F to re-fuse the internal cracks. I can send you a tested anneal schedule if you want, just let me know how thick the blank is. You will also need something to make a mold out of as the glass will flow some when you are doing the fusing (I'll include some molding suggestions with the anneal schedule if you want too.). Good luck. Cheers, Thomas Janstrom. Little Gems. http://tjlittlegems.com -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Francis J. O'Reilly Sent: Monday, 16 March 2009 2:53 AM To: atm at atmlist.net Subject: [ATM] Remelting glass I have a 12.25 inch old blank of questionable parentage that I got I don't remember when from I don't remember where. I believe that it is old pyrex. One side is fine, there are internal cracks on the other side. I intend to make a 12.25 inch flat for use in a small autocollimator. I would like to remelt and anneal the blank before I start in on the flat. I am finishing a number of projects now so I have some time. Does anyone know who might be able to remelt and anneal the glass. The flat will be my opus magnus when done (At least until my next project) I would like to have the internal issues cleared. That being said, I am aware that the internal cracks will not have much impact on the flat whatsoever. I just want them fixed and the annealing to be done to modern standards. Francis J. O'Reilly _______________________________________________ ATM mailing list http://www.atmlist.net/ From wa4guu at verizon.net Mon Mar 16 09:24:46 2009 From: wa4guu at verizon.net (Jerry) Date: Sun, 15 Mar 2009 20:24:46 -0400 Subject: [ATM] Remelting glass In-Reply-To: <01c601c9a5cc$05415950$0fc40bf0$@com> Message-ID: <0148317DCA12472983C6D278326A1BE1@D85SJB21> Francis, Are you sure that those are internal cracks? Pyrex can have visible swirls from pouring. I have seen this more in the golden colored blanks than in the white glass. Jerry From vorblesnak at peak.org Mon Mar 16 10:57:08 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Sun, 15 Mar 2009 18:57:08 -0700 (PDT) Subject: [ATM] 48 inch info and housekeeping Message-ID: <54698.4.242.238.107.1237168628.squirrel@webmail.peak.org> So it appears there is a general concern with me taking on this 48 inch disk. I suspect that much of the nay saying I have heard has to do with a misunderstanding about the scope of the project, either on my side or your side. But before I launch into long streams of text that are sufficient punishment for both sides .. some housekeeping. In an earlier posting I promised to weigh the foam mirrors. I don't remember why right now. 12 inch f7 .. 9 ounces 1/8th inch face plate 16 inch f3 .. 5 lbs ? inch face plate 19 inch f3 .. 5 lbs 1/8th inch face plate The glass I have on hand .. 1 - 28 inch diameter, ? inch thick plate. Tattletail glass for process testing 12 lbs 1 ? 36 inch diameter, ? inch thick plate. Tattletail glass for process testing. 15 lbs 3 ? 42 inch diameter, 3/8th inch thick plate. Mirror face plates. 50 lbs ea 1 ? 48 inch diameter, 3/8th inch thick plate. Mirror face plate. 60 lbs 10 pieces 4 inch thick glass foam. 18 inch x 24 inch rectangle. 8 lbs each. David Davis Toledo, OR 97391 From vorblesnak at peak.org Mon Mar 16 11:21:33 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Sun, 15 Mar 2009 19:21:33 -0700 (PDT) Subject: [ATM] David Davis.. 48 " disk with Glass foam backing Message-ID: <33313.4.242.238.107.1237170093.squirrel@webmail.peak.org> Russ wrote: > I and Andrew A. have discussed this application. It seems that the fusion > of the suface glass and the glass foam substrate is very stable. The > problem comes when you start to grind and polish. The problems start even before that Russ. Ignoring the problems with slumping and fusing the glass foam, it is not available in any size above 18 inches by 24 inches. > Even though the surface glass is slumped to a curve that is very close to > where you need to be. There must be some grinding and polishing going > on... Our first problem was side support of the foam substrate on a > grinding machine?? This stuff is not really very hard.. Duct tape. Three wraps of duct tape seals the foam just fine. It has good compressive strength, it just won't handle the abrasive movement of the fingers on the overarm pushing on the side of the disk. Duct tape handles that. Of course you could do tool on top. That is how I am doing the 12 inch. BTB: I got wrapped up in work and did not get back to the 12 inch this weekend so it did not get polished. When that is done it goes to Andrew for his purposes. If you would like one of these to grind on I will send one to you, but you should probably make the tool there. One of the things I am exploring is a glass foam tool. > Second problem was thickness of the surface glass. Yes it is slumped to a > certain F number but grinding and polishing will dig.. I think you had > that problem with a 1/4" surface glass. No, that was with a 1/8th inch face plate. The foam distorts badly when fused and the distortion is deeper than the thickness of the plate. We had hoped to use 1/8th inch plate but too much distortion. However, a slumped face plate glued to the foam works very well, as you will see when the 12 gets down to Andrew. That one hogged out with 120 grit and the total grind time to polish was just 6 hours. Hogging time was 45 minutes. I could have moved faster but I had no 220 for the intermediate step so I went from 120 to 400 and it took a while to get the tattle tail spot ground out. > David this is an excellent experiment, but as I and Andrew A. discussed > small proto's must be completed to the final figure in order to get to the > bigger experiment. Well .. I did smaller protos. I am doing an ultrathin here, not a glass foam composite. I will use the glass foam as the backer I could not find when I did the 15.5 ultrathin. I have polished out a lot of ultrathin slumped plate in the last few years. To be honest, I am not even sure I will attach the plate to the foam. I am leaning towards using the foam as a cell and buffer between the face plate and the scope mount. Even if that process does not work it will be a minor step to glue the glass to the foam and re-figure. .. snip .. > The glass foam is amazing but you can break it with your hand... > RUSS JOCOY David Davis Toledo, OR 97391 From vorblesnak at peak.org Mon Mar 16 11:31:14 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Sun, 15 Mar 2009 19:31:14 -0700 (PDT) Subject: [ATM] 48 inch process Message-ID: <35988.4.242.238.107.1237170674.squirrel@webmail.peak.org> The 48 inch ultrathin project has several facets that must be completed before I ever get to the point of putting a tool on the glass. 1.I have to build a kiln. 2.I have to make a slumping form in said kiln. 3.I have to slump the face plate 4.I have to assemble the glass foam back support 5.I have to shape the back support 6.I have to make a tool 7.I have to make a grinding machine 8.I have to get a lot of grit 9.Pitch If I don't start now it will be a long time before I can get it done. And I would like to have it done for the man that requested it by summer. I think I can do that. Kiln: It will be a one shot disposable kiln. I will have to make it a bit differently this time as I hope to use a different heat source. So the walls will not be just trapping heat, they will have to hold up some weight. I need some space between the walls and the project so the basic kiln ring will be 60 inches inside diameter. I will make the walls from stacked concrete building blocks and I will use ceramic wool to insulate and hold the heat in. The floor will be 2 inches of vermiculite topped with damp sand so that I can screed the ROC into the sand and have it hold that shape. That was a source of concern as I was unsure how I would negate the springiness of the vermiculite. I overcame that by purchasing some insulating fire bricks. They will rest on the garage floor with vermiculite around them and support the form ring. Should work. It will take 12 blocks to make the ring, 99 cents each. I have the wool, I have the heat source, I have the controller. I ain't got the space. I will need 72 inches for the ring and a couple of feet of clear space around the kiln. I will need the whole garage floor. I gotta clean the garage. David Davis Toledo, OR 97391 From jkoptic at juno.com Mon Mar 16 12:11:57 2009 From: jkoptic at juno.com (Jarvis Krumbein) Date: Sun, 15 Mar 2009 20:11:57 -0700 Subject: [ATM] Re melting glass Message-ID: <20090315.201157.376.0.jkoptic@juno.com> Francis, you probably have one of the old Pyrex blanks that Corning made. These generally had a lot of visible imperfections such as striah in the glass but were usually well annealed. I would not try to remelt or re anneal the blank but use it as is. I've done a number of these 12-1/4" as mirrors and never had any trouble with the glass other than breaking through a bubble or two that was to near the surface. You can always do a crossed polarizer test to look for strains in the glass to be sure. Jarvis Krumbein On Sun, 15 Mar 2009 12:52:31 -0400 "Francis J. O'Reilly" writes: > I have a 12.25 inch old blank of questionable parentage that I got I > don't remember when from I don't remember where. I believe that it > is old pyrex. > > One side is fine, there are internal cracks on the other side. I > intend to make a 12.25 inch flat for use in a small autocollimator. > > I would like to remelt and anneal the blank before I start in on the > flat. I am finishing a number of projects now so I have some time. > > Does anyone know who might be able to remelt and anneal the glass. > The flat will be my opus magnus when done (At least until my next > project) I would like to have the internal issues cleared. > > That being said, I am aware that the internal cracks will not have > much impact on the flat whatsoever. I just want them fixed and the > annealing to be done to modern standards. > > Francis J. O'Reilly > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > ____________________________________________________________ Click here to solve your love problems with the best love advice. http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTE8yx5qeISQhMha2hT4aaPfrGr0q3JVllfCvsZ8oadN4iDqBVZ80Q/ From dlwebb at canit.se Mon Mar 16 20:46:21 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Mon, 16 Mar 2009 12:46:21 +0100 (MET) Subject: [ATM] Maksutov-Cassegrain: Curvature of field In-Reply-To: <001001c9a4fa$675e6ab0$3758f804@Handsome> Message-ID: Thanks for these thoughts. Richard, Once again, I will need to think on your post for a couple days. The additional terms look useful. Vladimir, I encountered your website and looks like momumental undertaking. The section I encountered regarding Mak-Cass, section 11.1, was nice to see. It did not state field cuvature calculation. Everyone, a number of texts leave this out and so far I find no way for my version of Oslo (Osloedu) to automatically solve field curvature. This comes up because I have a design I believe to be rather good, but Oslo is giving spots far from what could be called diffraction limited, even on axis. Looking at the focus shift, spots get smaller by defocusing. Tolerances are rather tight and I can't afford to make any more big changes in the corrector I have been grinding. Dominic From dlwebb at canit.se Mon Mar 16 23:09:54 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Mon, 16 Mar 2009 15:09:54 +0100 (MET) Subject: [ATM] 48 inch info and housekeeping In-Reply-To: <54698.4.242.238.107.1237168628.squirrel@webmail.peak.org> Message-ID: On Sun, 15 Mar 2009 vorblesnak at peak.org wrote: > The glass I have on hand .. > > 1 - 28 inch diameter, ? inch thick plate. Tattletail glass for process > testing 12 lbs > 1 ? 36 inch diameter, ? inch thick plate. Tattletail glass for process > testing. 15 lbs > 3 ? 42 inch diameter, 3/8th inch thick plate. Mirror face plates. 50 lbs ea > 1 ? 48 inch diameter, 3/8th inch thick plate. Mirror face plate. 60 lbs > > 10 pieces 4 inch thick glass foam. 18 inch x 24 inch rectangle. 8 lbs each. > > David Davis > Toledo, OR 97391 I'll bite... a less than diffraction limited reflector can be extremely powerful tool. I actually use such a mirror, admittedly not every day, or even as often as some people say I should. This mirror resides in my bathroom and I purchased it dirt cheap in a department store. I use this spherical magnifying mirror those days when I shave. Mostly guys in here, so think on this a bit next time you shave in front of your favorite magnifying shaving mirror. After shaving (while shaving???), do a Ronchi test on that mirror. Optically ridiculous! Far worse than the worst mirror any of us have ever made. But it works great for shaving! I would urge you to think on sane applications for this mirror based on less than optimal surface profile. For instance, maybe something with very long focus that would not require a seep sagitta. Dominic From lopez at mv.mv.com Mon Mar 16 23:27:47 2009 From: lopez at mv.mv.com (Lawrence D. Lopez) Date: Mon, 16 Mar 2009 10:27:47 -0400 Subject: [ATM] 48 inch info and housekeeping In-Reply-To: References: Message-ID: <49BE61E3.3010109@mv.mv.com> I take exception to the direction this thread is taking. http://www.mv.com/users/lopez/contract/ldl.jpg Dominic-Luc Webb wrote: > On Sun, 15 Mar 2009 vorblesnak at peak.org wrote: > > >> The glass I have on hand .. >> >> 1 - 28 inch diameter, ? inch thick plate. Tattletail glass for process >> testing 12 lbs >> 1 ? 36 inch diameter, ? inch thick plate. Tattletail glass for process >> testing. 15 lbs >> 3 ? 42 inch diameter, 3/8th inch thick plate. Mirror face plates. 50 lbs ea >> 1 ? 48 inch diameter, 3/8th inch thick plate. Mirror face plate. 60 lbs >> >> 10 pieces 4 inch thick glass foam. 18 inch x 24 inch rectangle. 8 lbs each. >> >> David Davis >> Toledo, OR 97391 >> > > I'll bite... a less than diffraction limited reflector can > be extremely powerful tool. I actually use such a mirror, > admittedly not every day, or even as often as some people > say I should. This mirror resides in my bathroom and I > purchased it dirt cheap in a department store. I use this > spherical magnifying mirror those days when I shave. Mostly > guys in here, so think on this a bit next time you shave > in front of your favorite magnifying shaving mirror. After > shaving (while shaving???), do a Ronchi test on that mirror. > Optically ridiculous! Far worse than the worst mirror any of > us have ever made. But it works great for shaving! > > I would urge you to think on sane applications for this > mirror based on less than optimal surface profile. For > instance, maybe something with very long focus that would > not require a seep sagitta. > > Dominic > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > From vla at copper.net Mon Mar 16 23:36:48 2009 From: vla at copper.net (vladimir sacek) Date: Mon, 16 Mar 2009 10:36:48 -0400 Subject: [ATM] Maksutov-Cassegrain: Curvature of field References: Message-ID: <008c01c9a644$a4c9b800$4e5df804@Handsome> Dominic, > The section I encountered > regarding Mak-Cass, section 11.1, was nice to see. It > did not state field cuvature calculation. 11.1 is not the link I've posted: http://www.telescope-optics.net/MCT_off_axis.htm If you open up this link, it takes you to 11.8.2 and near the bottom it gives the equation for MCT field curvature (Eq. 133): (1/Rm)=(1/Rp)+4a with Rm being the best (median) field curvature, Rp the system's Petzval and "a" the system coefficient of astigmatism (for which is given exact formula, and approximation). >From what I see, best surface curvature in a typical MCT (either Gregory or w/separated secondary) tend to be nominally quite close to the secondary mirror radius of curvature. Vla From hermit at outofoptions.org Mon Mar 16 23:49:24 2009 From: hermit at outofoptions.org (hermit) Date: Mon, 16 Mar 2009 10:49:24 -0400 Subject: [ATM] 48 inch info and housekeeping In-Reply-To: References: Message-ID: <49BE66F4.50207@outofoptions.org> Dominic-Luc Webb wrote: > so think on this a bit next time you shave Shave? I'm not familiar with this concept myself. :D Has he said how these mirrors perform in the field? I'd be worried about differential cooling between the top plate and the thicker 'foam'. Ken Lowther From melockwo at uiuc.edu Tue Mar 17 01:46:06 2009 From: melockwo at uiuc.edu (Mike Lockwood) Date: Mon, 16 Mar 2009 10:46:06 -0600 Subject: [ATM] what to do best? In-Reply-To: <3B091A48D76E4452ADEF3759C311CCB5@niks03981037eb> References: <49BAC2CA.40609@hetnet.nl> <3B091A48D76E4452ADEF3759C311CCB5@niks03981037eb> Message-ID: <49BE824E.8080108@uiuc.edu> Hi, Jan van Gastel wrote: > I am not good at the accented pressure method. I have decided to go > with Mike Lockwood's idea and went back to a sphere to start again. Just to clarify, what I said was to go back TOWARD a sphere (not TO a sphere), stopping when the outer zone had ~60% correction, and then resume figuring from there. Jerry wrote: > I recommend only working one zone at a time so that you can see > exactly what happens compared to what you think will happen when you > work a particular zone. Wait until you have gained much experience > before fixing multiple problems in one session. I've made a LOT of mirrors and I can't work one zone at a time! Then again the zones I measure are fairly narrow, and one wouldn't want to work only one at a time or else the zones would probably end up with large slope errors. I'm assuming you meant work on one "feature" at a time, and not literally a measured zone. Mike Lockwood From dlwebb at canit.se Tue Mar 17 00:47:14 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Mon, 16 Mar 2009 16:47:14 +0100 (MET) Subject: [ATM] Maksutov-Cassegrain: Curvature of field In-Reply-To: <008c01c9a644$a4c9b800$4e5df804@Handsome> Message-ID: On Mon, 16 Mar 2009, vladimir sacek wrote: > Dominic, > > > The section I encountered > > regarding Mak-Cass, section 11.1, was nice to see. It > > did not state field cuvature calculation. > > 11.1 is not the link I've posted: Understood. I only meant I encountered that section. I am reading the link you sent and thinking on it now. Thanks! Dominic From jhm.vangastel at ziggo.nl Tue Mar 17 01:28:35 2009 From: jhm.vangastel at ziggo.nl (Jan van Gastel) Date: Mon, 16 Mar 2009 17:28:35 +0100 Subject: [ATM] what to do best? References: <49BAC2CA.40609@hetnet.nl> <3B091A48D76E4452ADEF3759C311CCB5@niks03981037eb> <49BE824E.8080108@uiuc.edu> Message-ID: <4FDA45C9133A44DD8DE83E1FE0A110AD@niks03981037eb> OK, then I understood your advice wrong, Mike. But no problem at all. I just started parabolizing again from a sphere. I do short sessions now to be able to see what happens and to have as much control as possible. Jan http://members.ziggo.nl/jhm.vangastel/Astronomy/ ----- Original Message ----- From: "Mike Lockwood" To: Sent: Monday, March 16, 2009 17:46 Subject: Re: [ATM] what to do best? > Hi, > > Jan van Gastel wrote: >> I am not good at the accented pressure method. I have decided to go >> with Mike Lockwood's idea and went back to a sphere to start again. > > Just to clarify, what I said was to go back TOWARD a sphere (not TO a > sphere), stopping when the outer zone had ~60% correction, and then resume > figuring from there. > > Jerry wrote: >> I recommend only working one zone at a time so that you can see >> exactly what happens compared to what you think will happen when you >> work a particular zone. Wait until you have gained much experience >> before fixing multiple problems in one session. > > I've made a LOT of mirrors and I can't work one zone at a time! > > Then again the zones I measure are fairly narrow, and one wouldn't want to > work only one at a time or else the zones would probably end up with large > slope errors. > > I'm assuming you meant work on one "feature" at a time, and not literally > a measured zone. > > Mike Lockwood > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From vorblesnak at peak.org Tue Mar 17 05:11:51 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Mon, 16 Mar 2009 13:11:51 -0700 (PDT) Subject: [ATM] 48 inch info and housekeeping Message-ID: <17666.159.121.96.200.1237234311.squirrel@webmail.peak.org> The finished mirror will be an f3. The scope that is planned is an instrument scope. The primary processes will be photometry, spectroscopy. The gentleman that requested it would be happy if I can get it within 1 wave. Of course I am going to try for better than that, he can always defocus a bit. I remembered why I was suppose to weigh the mirrors. A general concern is the weight of the mirror and the tool. Based on the numbers I provided the weight of the mirror would be in the range of 140 lbs. The tool will depend on the material chosen to make it. I am working on a glass foam tool. Should that work out the total weight of mirror and tool would be less than 300 lbs, maybe less than 250. If that holds true I can just extend my existing grinding machine instead of building a new one. It would be one hell of a shaving mirror. David Davis Toledo, OR 97391 From rmay at nethere.com Tue Mar 17 08:22:37 2009 From: rmay at nethere.com (Bob May) Date: Mon, 16 Mar 2009 15:22:37 -0800 Subject: [ATM] Remelting old glass References: <20090315221054.2SU74.250479.root@cdptpa-web08-z01> Message-ID: <002e01c9a68e$195c0e40$8f78fea9@amd> I'd more believe about $200 or so for a new blank of full thickness. If it really is cracks (silvery reflective clamshell looking things) in the glass, I'd be carefull but if it more looks like waves then it is pretty normal for much of pyrex as mirror blanks don't need to have optically clear insides to work well. I would do a strain check just to make sure that there is no strain in the piece of glass as that will make for all kinds of problems when you are done. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Tue Mar 17 08:32:12 2009 From: rmay at nethere.com (Bob May) Date: Mon, 16 Mar 2009 15:32:12 -0800 Subject: [ATM] 48 inch info and housekeeping References: <17666.159.121.96.200.1237234311.squirrel@webmail.peak.org> Message-ID: <003f01c9a68f$70085c20$8f78fea9@amd> Dave, you really don't want to do a full sized tool but rather something a bit smaller. Doing all of your work with the mirror on the bottom will be what you want to do. so the mirror will not have any problems getting really local pressure on the foam which will quickly break down if you do. Polishing definetely will need to be done with a small tool as the forces needed will probably just destroy the foam from the shear forces involved. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From vorblesnak at peak.org Tue Mar 17 12:49:57 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Mon, 16 Mar 2009 20:49:57 -0700 (PDT) Subject: [ATM] Polishing foam Message-ID: <48027.4.242.144.7.1237261797.squirrel@webmail.peak.org> Yes, it has come to this. I am polishing a foam mirror. Whats more I am doing a lousy job of it and yet I still get ronchi lines. Very scary ronchi lines but lines. Much polishing left to do but enough resolution to determine it is a 12.5 inch mirror with a 90 inch focal length. f7.5 in my math is correct. The front plate is 1/8th inch plate window glass. The backer is glass foam. The glue is Gorilla. I have about three hours into the polish right now. I need a full size lap. I been doing it with a 6 inch lap. Machines are just wonderful. It is not my intent to make a telescope mirror with this piece but rather to get a polish on it so it can be tested for distortion etc due to environmental changes. I should be able to get a sphere out of it. This mirror has been worked tool on top from the beginning. It has rocked on the plate to an extent and been splashed clean and wiped down with a towel. I have not been careful or kind but if it is going to fail during grind I wanna do it. I never took the time to finish the grind above 400 so it has a spot about the size of a dime that never got ground. One edge missing, cut off to expose the glue joint. It is a dog of a mirror at best. Russ? This one goes down to Andrew for environment work and true testing, not that 50 line ronchi stuff I am infamous for. And I have one here with your name on it if you want to grind one. Always happy to infect another soul. David Davis Toledo, OR 97391 From tcohen at blakeglobal.com Tue Mar 17 13:27:40 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Mon, 16 Mar 2009 21:27:40 -0700 Subject: [ATM] Some improvement seen In-Reply-To: <730905.99337.qm@web54501.mail.re2.yahoo.com> References: <430008.62442.qm@web54501.mail.re2.yahoo.com> <730905.99337.qm@web54501.mail.re2.yahoo.com> Message-ID: As shown in the Ronchigrams http://tinyurl.com/c2eeww I still have much more work, but at least I think I'm making progress! The grating is 150 lines per inch. I've switched to black rouge to help smooth out the ripples and generally slow down the action. For those of you who haven't tried black rouge, it's worth a try. I find it very uniform in its action, unlike cerium oxide, which tends to go through various phases of temperament during each wet. There is a silky smooth viscous resistance that remains consistent throughout the wet. The wets seem to last a little longer with the black rough - perhaps because it's more enjoyable to work with toward the end of the wet, and one doesn't want to stop but keep pushing on. I'm hoping that by going to a slower polishing agent, I'll tend toward less, low-frequency ripple and better blending. From mbartels at bbastrodesigns.com Tue Mar 17 13:32:45 2009 From: mbartels at bbastrodesigns.com (Mel Bartels) Date: Mon, 16 Mar 2009 21:32:45 -0700 Subject: [ATM] Some improvement seen In-Reply-To: References: <430008.62442.qm@web54501.mail.re2.yahoo.com> <730905.99337.qm@web54501.mail.re2.yahoo.com> Message-ID: <005901c9a6b9$6f29a2d0$4d7ce870$@com> >>> As shown in the Ronchigrams http://tinyurl.com/c2eeww I still have much more work, but at least I think I'm making progress! The grating is 150 lines per inch. I've switched to black rouge to help smooth out the ripples <<< So you're still working to reduce astigmatism? The last set of images appear to contain significant astigmatic. Mel Bartels From tcohen at blakeglobal.com Tue Mar 17 13:51:18 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Mon, 16 Mar 2009 21:51:18 -0700 Subject: [ATM] Some improvement seen In-Reply-To: <005901c9a6b9$6f29a2d0$4d7ce870$@com> References: <430008.62442.qm@web54501.mail.re2.yahoo.com> <730905.99337.qm@web54501.mail.re2.yahoo.com> <005901c9a6b9$6f29a2d0$4d7ce870$@com> Message-ID: <2722ABC7C3EE4E1C83AF15DBB5D45882@BLAKESF.LOCAL> Yes, there is still a lot of astigmatism - more than I realized when I said that I had removed most of it. -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Mel Bartels Sent: Monday, March 16, 2009 9:33 PM To: atm at atmlist.net Subject: Re: [ATM] Some improvement seen >>> As shown in the Ronchigrams http://tinyurl.com/c2eeww I still have much more work, but at least I think I'm making progress! The grating is 150 lines per inch. I've switched to black rouge to help smooth out the ripples <<< So you're still working to reduce astigmatism? The last set of images appear to contain significant astigmatic. Mel Bartels _______________________________________________ ATM mailing list http://www.atmlist.net/ From foreilly at verizon.net Tue Mar 17 21:27:34 2009 From: foreilly at verizon.net (Francis J. O'Reilly) Date: Tue, 17 Mar 2009 08:27:34 -0400 Subject: [ATM] Polishing foam April first References: <48027.4.242.144.7.1237261797.squirrel@webmail.peak.org> Message-ID: <535A6194BFA24A73A13F1FF48B09FDB6@HELENYLCMWAV95> I presume that this entire thread and the related 48 inch thread are early April Fools jokes. Francis J. O'Reilly ----- Original Message ----- From: To: Sent: Monday, March 16, 2009 11:49 PM Subject: [ATM] Polishing foam > Yes, it has come to this. I am polishing a foam mirror. Whats more I am > doing a lousy job of it and yet I still get ronchi lines. Very scary > ronchi lines but lines. Much polishing left to do but enough resolution to > determine it is a 12.5 inch mirror with a 90 inch focal length. f7.5 in > my math is correct. > > The front plate is 1/8th inch plate window glass. The backer is glass > foam. The glue is Gorilla. I have about three hours into the polish right > now. I need a full size lap. I been doing it with a 6 inch lap. Machines > are just wonderful. > > It is not my intent to make a telescope mirror with this piece but rather > to get a polish on it so it can be tested for distortion etc due to > environmental changes. I should be able to get a sphere out of it. This > mirror has been worked tool on top from the beginning. It has rocked on > the plate to an extent and been splashed clean and wiped down with a > towel. I have not been careful or kind but if it is going to fail during > grind I wanna do it. I never took the time to finish the grind above 400 > so it has a spot about the size of a dime that never got ground. One edge > missing, cut off to expose the glue joint. It is a dog of a mirror at > best. > > Russ? This one goes down to Andrew for environment work and true testing, > not that 50 line ronchi stuff I am infamous for. And I have one here with > your name on it if you want to grind one. Always happy to infect another > soul. > > David Davis > Toledo, OR 97391 > > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From richard at foucault.co.uk Tue Mar 17 23:33:35 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Tue, 17 Mar 2009 14:33:35 +0000 Subject: [ATM] C1 glass Message-ID: <322007267.20090317143335@foucault.co.uk> Hello ATMers, Does anybody have refraction and dispersion data for an old glass type C1 please? -- Best regards, Richard in the UK From vorblesnak at peak.org Tue Mar 17 23:42:52 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Tue, 17 Mar 2009 07:42:52 -0700 (PDT) Subject: [ATM] Polishing foam April first In-Reply-To: <535A6194BFA24A73A13F1FF48B09FDB6@HELENYLCMWAV95> References: <48027.4.242.144.7.1237261797.squirrel@webmail.peak.org> <535A6194BFA24A73A13F1FF48B09FDB6@HELENYLCMWAV95> Message-ID: <34917.159.121.96.200.1237300972.squirrel@webmail.peak.org> No, no it is all real. The glass / glass foam mirror is rapidly polishing out. I was measuring the Hindle machine last night and I am confident I can size it up to handle the 48. I have been reviewing the various articles in ATM1 by Ritchey and Hindle on machine design and operation. Here is the Pasadena meeting for the initiative .. http://aas.org/meetings/aas214/event_workshop_alt-az.php Here is the home page .. http://www.altazinitiative.org/ The initiative just released a position paper to the National Academy of Science. It is all far far too real. All I have to do is deliver a mirror, if I can. I hope to have it in Pasadena. Gonna be a push. David Davis Toledo, OR 97391 > I presume that this entire thread and the related 48 inch thread are early > April Fools jokes. > > Francis J. O'Reilly > ----- Original Message ----- > From: > To: > Sent: Monday, March 16, 2009 11:49 PM > Subject: [ATM] Polishing foam > > >> Yes, it has come to this. I am polishing a foam mirror. Whats more I am >> doing a lousy job of it and yet I still get ronchi lines. Very scary >> ronchi lines but lines. Much polishing left to do but enough resolution >> to >> determine it is a 12.5 inch mirror with a 90 inch focal length. f7.5 in >> my math is correct. >> >> The front plate is 1/8th inch plate window glass. The backer is glass >> foam. The glue is Gorilla. I have about three hours into the polish >> right >> now. I need a full size lap. I been doing it with a 6 inch lap. Machines >> are just wonderful. >> >> It is not my intent to make a telescope mirror with this piece but >> rather >> to get a polish on it so it can be tested for distortion etc due to >> environmental changes. I should be able to get a sphere out of it. This >> mirror has been worked tool on top from the beginning. It has rocked on >> the plate to an extent and been splashed clean and wiped down with a >> towel. I have not been careful or kind but if it is going to fail during >> grind I wanna do it. I never took the time to finish the grind above 400 >> so it has a spot about the size of a dime that never got ground. One >> edge >> missing, cut off to expose the glue joint. It is a dog of a mirror at >> best. >> >> Russ? This one goes down to Andrew for environment work and true >> testing, >> not that 50 line ronchi stuff I am infamous for. And I have one here >> with >> your name on it if you want to grind one. Always happy to infect another >> soul. >> >> David Davis >> Toledo, OR 97391 >> >> >> >> >> _______________________________________________ >> ATM mailing list http://www.atmlist.net/ >> > > > From dlwebb at canit.se Wed Mar 18 00:28:22 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Tue, 17 Mar 2009 16:28:22 +0100 (MET) Subject: [ATM] C1 glass In-Reply-To: <322007267.20090317143335@foucault.co.uk> Message-ID: On Tue, 17 Mar 2009, Richard in the UK wrote: > Hello ATMers, > > Does anybody have refraction and dispersion data for an old glass type > C1 please? > > -- > Best regards, > Richard in the UK This should be in Cat# 4 from Hayward Glass Corp, 217 Magnolia Ave, Whittier, CA, USA. I do not have this catalog. The only info I know of are in two papers by Norman A Burts in Nov and Dec 1957 Sky and Telescope (Gleanings for ATMs). I believe he cites in the Dec issue refractive index values for C-1 from that catalog for mercury 5461 green (1.5252) and sodium yellow (1.5230). These values were posted to the list on 23 Mar 1998 by Roger (Sinnott) at S&T. Roger states that the Club ordered C-1. I made phone calls and other investigations at which time I was introduced to the name BSC-2 and told this was same or equivalent. I do not think Hayward Glass Corp exists anymore, but I think someone at Newport Glass I spoke with new about it. I finally tracked down the two Burts articles and have been able to confirm the values from Roger at S&T. I have **NOT** been able to confirm that the Mak Club actually ordered C-1. It is possible that BSC-2 was actually what was ordered by the Club or what appeared on a receipt or some such. Somewhere out there is a letter to the Mak Club about this order. This I know. Dominic From wa4guu at verizon.net Wed Mar 18 00:31:44 2009 From: wa4guu at verizon.net (Jerry) Date: Tue, 17 Mar 2009 11:31:44 -0400 Subject: [ATM] Some improvement seen In-Reply-To: Message-ID: I guess that this is the 23 X 3/4 inch mirror? What f:#? What size lap are you using? -----Original Message----- From: Ted Cohen As shown in the Ronchigrams http://tinyurl.com/c2eeww I still have much more work, but at least I think I'm making progress! The grating is 150 lines per inch. From rflrs at rcn.com Wed Mar 18 00:43:41 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Tue, 17 Mar 2009 10:43:41 -0500 Subject: [ATM] C1 glass In-Reply-To: References: Message-ID: <49BFC52D.1030303@rcn.com> Dominic-Luc Webb wrote: > > > This should be in Cat# 4 from Hayward Glass Corp, 217 Magnolia > Ave, Whittier, CA, USA. I do not have this catalog. The only > info I know of are in two papers by Norman A Burts in Nov > and Dec 1957 Sky and Telescope (Gleanings for ATMs). I > believe he cites in the Dec issue refractive index values > for C-1 from that catalog for mercury 5461 green (1.5252) > and sodium yellow (1.5230). These values were posted to the > list on 23 Mar 1998 by Roger (Sinnott) at S&T. Roger states > that the Club ordered C-1. I made phone calls and other > investigations at which time I was introduced to the > name BSC-2 and told this was same or equivalent. I do not > think Hayward Glass Corp exists anymore, but I think someone > at Newport Glass I spoke with new about it. They might. The website (glass compendium) lists C1 as 523585. They said it came from the Hayward catalog. Maybe they can send you a copy of the necessary page. From dlwebb at canit.se Wed Mar 18 00:54:36 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Tue, 17 Mar 2009 16:54:36 +0100 (MET) Subject: [ATM] C1 glass In-Reply-To: Message-ID: BTW... there is something currently referred to as spectacle crown C-1 that has a stated RI of 1.523... Dominic From jack.swaton at starryhost.com Wed Mar 18 01:03:13 2009 From: jack.swaton at starryhost.com (Jack Swaton @ Starry Host) Date: Tue, 17 Mar 2009 09:03:13 -0700 Subject: [ATM] Preference on RFT In-Reply-To: <380-22009301554057924@M2W019.mail2web.com> References: <380-22009301554057924@M2W019.mail2web.com> Message-ID: <323EC3046BF34B8283AD02793355AB4E@MRBNOTEBOOK> That's what I was afraid of! Here's a follow-up question: Is there a better option for scope choice which starts out as RFT but can handle barlows and magnification better to be able to view planets better? I know I'm shooting for the perfect scope, but hey, I might as well be intelligent about this! Thanks, Jack -----Original Message----- From: astroguy at nas.com [mailto:astroguy at nas.com] Sent: Saturday, March 14, 2009 10:41 PM To: jack.swaton at starryhost.com; atm at atmlist.net Subject: RE: [ATM] Preference on RFT I absolutely love my my 5" f/10 D&G refractor. It is simply, wonderful, fantastic, incredible, super, duper, great, the BEST!! Purrrrfect for planets!!! I absolutely love my my 6" f/5 Mak/Newt. It is simply, wonderful, fantastic, incredible, super, duper, great, the BEST!! Purrrrfect as an RFT!!! So, now you have your answer, the perfect scope..........s!! And one more thought. Several years ago, was observing at RTMC with Roland Christen of AstroPhysics fame. We used his 6" scope to chase down Pluto. Not only did we find Pluto but we could look directly at the "planet" and see a solid image. Pluto is much more evasive in most scopes. Conclusion: Refractor, Mak/Newt ...................... YES. Kreig Original Message: ----------------- From: Jack Swaton @ Starry Host jack.swaton at starryhost.com Date: Sat, 14 Mar 2009 22:06:02 -0700 To: atm at atmlist.net Subject: [ATM] Preference on RFT Does anybody have a preference on scopes for a given 6" aperture? Let's say I had a $1,000 (which unfortunately I don't) to spend on a Mak Newt or a 150mm refractor (this would obviously be a Meade/Celestron/etc). 1) Which would have better contrast, 2) Which would have pin-pointier stars 3) Which would have better light throughput? 4) Can a minus violet filter make the refractor more apo-like? ' Let's say they were both short focal lengths: 1) Would one respond better to barlows for better planetary visual observing? Let's say they were both long focal lengths.would one be better as an RFT scope? The reason why I'm asking is that as I grow older in my observing, my tastes changes. 13 inch scopes become too unwieldy and inexpensive refractors unacceptable with a heavy Denk bino or my family requires ultrafast observing sessions or. So I'm looking to acquire optics to build a small scope and have not had the opportunity to look through different scopes in several years. I want the perfect scope for that lovely RFT experience with black sky and pinpoint stars but that can also wow folks with the moon and planets. In short, I want the perfect scope. :-) If I go refractor, I'll probably build a bent light path so I can control the eyepiece elevation. If I go Mak Newt (or other design). I'll have to punt and learn what I can do with those. Thanks, Jack Swaton Starry Host _______________________________________________ ATM mailing list http://www.atmlist.net/ -------------------------------------------------------------------- mail2web.com - What can On Demand Business Solutions do for you? http://link.mail2web.com/Business/SharePoint From tcohen at blakeglobal.com Wed Mar 18 02:07:26 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Tue, 17 Mar 2009 10:07:26 -0700 Subject: [ATM] Some improvement seen In-Reply-To: References: Message-ID: <6DAA099A9AFF4D0ABCC30E6E8EA4F366@BLAKESF.LOCAL> Re: >> I guess that this is the 23 X 3/4 inch mirror? >> What f:#? >> What size lap are you using? Yes, 23" x 3/4" floating in 3/8" layer of pitch with 1" thick aluminum plate backing. The focal ratio has crept down to about 3.9 (I was originally targeting 4.75) The tool is dental stone approximately 4"-5" thick about 11" diameter (40%-50% of mirror diameter). Worked TOT 55-gallon barrel with concrete platform. My target correction is 1/3-1/4 wave peak to valley with no turned edge. I anticipate another six months of figuring at the rate I'm going. My biggest worry at this point is the telescope mount. -----Original Message----- From: Ted Cohen As shown in the Ronchigrams http://tinyurl.com/c2eeww I still have much more work, but at least I think I'm making progress! The grating is 150 lines per inch. _______________________________________________ ATM mailing list http://www.atmlist.net/ From anishmangal2002 at gmail.com Wed Mar 18 02:12:43 2009 From: anishmangal2002 at gmail.com (Anish Mangal) Date: Tue, 17 Mar 2009 22:42:43 +0530 Subject: [ATM] Emoticons for telescopes. Message-ID: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> Hi, I was wondering if anyone's ever used emoticon text to describe telescopes ;) I came up with a few (assuming target FOV at right) Newtonian reflector : ( \ Simple refractor : o O Cassegrain : ( | Mak-Cass : ( ( Maybe these can be a part of ATM lingo... Cheers! Anish Mangal From hermit at outofoptions.org Wed Mar 18 02:15:45 2009 From: hermit at outofoptions.org (hermit) Date: Tue, 17 Mar 2009 13:15:45 -0400 Subject: [ATM] Emoticons for telescopes. In-Reply-To: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> References: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> Message-ID: <49BFDAC1.1010005@outofoptions.org> We have enough trouble explaining MOT and TOT. Ken Lowther Anish Mangal wrote: > Hi, > > I was wondering if anyone's ever used emoticon text to describe telescopes > ;) > > I came up with a few (assuming target FOV at right) > > Newtonian reflector : ( \ > Simple refractor : o O > Cassegrain : ( | > Mak-Cass : ( ( > > > Maybe these can be a part of ATM lingo... > > Cheers! > Anish Mangal > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From shane at ct-astronomer.com Wed Mar 18 02:18:42 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Tue, 17 Mar 2009 13:18:42 -0400 Subject: [ATM] Emoticons for telescopes. In-Reply-To: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> References: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> Message-ID: <5E9230B8-8C5E-47E5-B62F-B1EF0A6817D8@ct-astronomer.com> I like it. Here's my latest paraboloid attempt for my newt: { \ There's a hole in the middle, and TUE. What stroke? LOL! Shane LaPierre On Mar 17, 2009, at 1:12 PM, Anish Mangal wrote: > Hi, > > I was wondering if anyone's ever used emoticon text to describe > telescopes > ;) > > I came up with a few (assuming target FOV at right) > > Newtonian reflector : ( \ > Simple refractor : o O > Cassegrain : ( | > Mak-Cass : ( ( > > > Maybe these can be a part of ATM lingo... > > Cheers! > Anish Mangal > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From djd521 at verizon.net Wed Mar 18 02:19:35 2009 From: djd521 at verizon.net (Don D'Egidio) Date: Tue, 17 Mar 2009 13:19:35 -0400 Subject: [ATM] Emoticons for telescopes. References: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> Message-ID: <0178D1501BC94035A0F2C980C84BD44A@donaldp4> But with most of the emoticons I've seen you would tilt your head to the left to view them. :-) Don ----- Original Message ----- From: "Anish Mangal" To: "ATM Superheros" Sent: Tuesday, March 17, 2009 1:12 PM Subject: [ATM] Emoticons for telescopes. > Hi, > > I was wondering if anyone's ever used emoticon text to describe telescopes > ;) > > I came up with a few (assuming target FOV at right) > > Newtonian reflector : ( \ > Simple refractor : o O > Cassegrain : ( | > Mak-Cass : ( ( > > > Maybe these can be a part of ATM lingo... > > Cheers! > Anish Mangal > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From richard at foucault.co.uk Wed Mar 18 02:20:34 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Tue, 17 Mar 2009 17:20:34 +0000 Subject: [ATM] C1 glass In-Reply-To: <49BFC52D.1030303@rcn.com> References: <49BFC52D.1030303@rcn.com> Message-ID: <1984997415.20090317172034@foucault.co.uk> Hello Richard, Tuesday, March 17, 2009, 3:43:41 PM, you wrote: > They might. The website (glass compendium) lists C1 as > 523585. There's a Bausch and Lomb 523586 on Bob May's web site with the following characteristics : type : 523586 Vd : 58.6 Wl n 1014 1.5130 766.5 1.51729 656.3 1.52036 589.3 1.52300 587.6 1.52307 546.1 1.52520 486.1 1.52929 435.8 1.53415 434.1 1.53435 404.7 1.53819 365.0 1.54505 The Abbe is only 0.1 out and the two spot points match with Dominic's info, so i am going to assume this is the one. Thanks chaps. -- Best regards, Richard in the UK From rflrs at rcn.com Wed Mar 18 02:57:16 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Tue, 17 Mar 2009 12:57:16 -0500 Subject: [ATM] C1 glass In-Reply-To: <1984997415.20090317172034@foucault.co.uk> References: <49BFC52D.1030303@rcn.com> <1984997415.20090317172034@foucault.co.uk> Message-ID: <49BFE47C.6020002@rcn.com> Richard in the UK wrote: > Hello Richard, > > Tuesday, March 17, 2009, 3:43:41 PM, you wrote: > >> They might. The website (glass compendium) lists C1 as >> 523585. > > There's a Bausch and Lomb 523586 on Bob May's web site with the > following characteristics : > > type : 523586 > Vd : 58.6 > > Wl n > 1014 1.5130 > 766.5 1.51729 > 656.3 1.52036 > 589.3 1.52300 > 587.6 1.52307 > 546.1 1.52520 > 486.1 1.52929 > 435.8 1.53415 > 434.1 1.53435 > 404.7 1.53819 > 365.0 1.54505 > > The Abbe is only 0.1 out and the two spot points match with Dominic's > info, so i am going to assume this is the one. Thanks chaps. > Maybe you can just use the model glass capability (using "normal", i.e.: 1.523,58.5, and 0.0 dpgf): 0.365015 0.404656 0.434100 0.435834 0.486133 0.546074 1.54520402 1.53816930 1.53429269 1.53409115 1.52921644 1.52513222 0.587562 0.589294 0.656273 0.766500 1.013980 1.52300178 1.52292212 1.52027984 1.51722107 1.51321517 if you think it would be close enough. From wa4guu at verizon.net Wed Mar 18 02:57:50 2009 From: wa4guu at verizon.net (Jerry) Date: Tue, 17 Mar 2009 13:57:50 -0400 Subject: [ATM] Emoticons for telescopes. In-Reply-To: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> Message-ID: <0A7DB16A250F4E8ABD56A62758A4678E@D85SJB21> Isn't that one already used for "aperture fever"? -----Original Message----- From: Anish Mangal Subject: [ATM] Emoticons for telescopes. I was wondering if anyone's ever used emoticon text to describe telescopes ;) I came up with a few (assuming target FOV at right) Simple refractor : o O From anishmangal2002 at gmail.com Wed Mar 18 03:03:11 2009 From: anishmangal2002 at gmail.com (Anish Mangal) Date: Tue, 17 Mar 2009 23:33:11 +0530 Subject: [ATM] Emoticons for telescopes. In-Reply-To: <0A7DB16A250F4E8ABD56A62758A4678E@D85SJB21> References: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> <0A7DB16A250F4E8ABD56A62758A4678E@D85SJB21> Message-ID: <47eee29a0903171103w5e93de4l953dcbd8b2a9c055@mail.gmail.com> Good one Jerry! here's one for accentuated aperture fever " . o O " Anish Mangal On Tue, Mar 17, 2009 at 11:27 PM, Jerry wrote: > Isn't that one already used for "aperture fever"? > > -----Original Message----- > From: Anish Mangal > Subject: [ATM] Emoticons for telescopes. > > I was wondering if anyone's ever used emoticon text to describe telescopes > ;) > > I came up with a few (assuming target FOV at right) > > Simple refractor : o O > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From richard at foucault.co.uk Wed Mar 18 03:09:42 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Tue, 17 Mar 2009 18:09:42 +0000 Subject: [ATM] C1 glass In-Reply-To: <49BFE47C.6020002@rcn.com> References: <49BFC52D.1030303@rcn.com> <1984997415.20090317172034@foucault.co.uk> <49BFE47C.6020002@rcn.com> Message-ID: <1075394653.20090317180942@foucault.co.uk> Hello Richard, Tuesday, March 17, 2009, 5:57:16 PM, you wrote: > Maybe you can just use the model glass capability (using > "normal", i.e.: 1.523,58.5, and 0.0 dpgf): Yes, but to model it I would need to know the Abbe, which I did not until you posted the 6 digit reference. Having got that, it took about 2 minutes to find the real data, which is always preferable IMO. -- Best regards, Richard in the UK From dlwebb at canit.se Wed Mar 18 03:37:57 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Tue, 17 Mar 2009 19:37:57 +0100 (MET) Subject: [ATM] C1 glass In-Reply-To: <1984997415.20090317172034@foucault.co.uk> Message-ID: On Tue, 17 Mar 2009, Richard in the UK wrote: > Hello Richard, > > Tuesday, March 17, 2009, 3:43:41 PM, you wrote: > > > They might. The website (glass compendium) lists C1 as > > 523585. > > There's a Bausch and Lomb 523586 on Bob May's web site with the > following characteristics : > > type : 523586 > Vd : 58.6 > > Wl n > 1014 1.5130 > 766.5 1.51729 > 656.3 1.52036 > 589.3 1.52300 > 587.6 1.52307 > 546.1 1.52520 > 486.1 1.52929 > 435.8 1.53415 > 434.1 1.53435 > 404.7 1.53819 > 365.0 1.54505 > > The Abbe is only 0.1 out and the two spot points match with Dominic's > info, so i am going to assume this is the one. Thanks chaps. > > -- > Best regards, > Richard in the UK I am no expert in this subject, but I once read on Sellmeier equations and had the idea that glass follows a common equation and so if this glass has two points that are same, they are almost certainly same glass. Dominic From richard at foucault.co.uk Wed Mar 18 04:12:55 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Tue, 17 Mar 2009 19:12:55 +0000 Subject: [ATM] C1 glass In-Reply-To: References: <1984997415.20090317172034@foucault.co.uk> Message-ID: <106148413.20090317191255@foucault.co.uk> Hello Dominic-Luc, Tuesday, March 17, 2009, 6:37:57 PM, you wrote: > On Tue, 17 Mar 2009, Richard in the UK wrote: > I am no expert in this subject, but I once read on > Sellmeier equations and had the idea that glass > follows a common equation and so if this glass > has two points that are same, they are almost > certainly same glass. Possibly, but you can draw a lot of different curves through 2 points. There are at least 12 different equations used for representing n against w, including several from each of Sellmeier, Hertzberger, Conrady and others. -- Best regards, Richard in the UK From matt at considine.net Wed Mar 18 04:47:26 2009 From: matt at considine.net (Matt Considine) Date: Tue, 17 Mar 2009 15:47:26 -0400 Subject: [ATM] C1 glass Message-ID: <49BFFE4E.2090005@considine.net> I checked through the early issues of the Mak Circulars. They ordered their corrector blanks from Hayward and got were looking at BSC-2. (per Circular #1 and #7; nD 1.5170 +/- 0.001, V 64.5 +/- .4). Mirror blanks were ordered from Corning. That said, there was a publication entitled "Characteristics of Commercial Optical Glass" from the Los Alamos Scientific Laboratory of The University of California. Dated March 20, 1951 (labeled LA-1222; author Berlyn Brixner) it contains data from Hayward Catalog #2 (March 1948). The glasses available are listed by serial number. So I guess it's possible that "C1" refers to serial number 1 in the catalog? (A guess, as I don't know the genesis of this question). Nevertheless, here is the data they list for that and for #4 (which is the 523585 referenced in this thread). The inital blocks of data I think were used in their extrapolation/checking of refractive indices. The collected list of six refractive indices is near the end, just before the constants used in the Hartmann formula for that particular glass. Hope this helps, Matt Glass S/N 1 4 Cat # 511635 523585 p11 nC 150860 152035 Vc 9596 8910 (C-B)/(e-B) 16980 16780 (e-C)/(e-B) 8301 8321 e-B 00529 00583 n/V 01572 01706 p26 ne 151300 152521 Ve 4097 3746 (e-C)/(G'-c) 35140 34660 (G'-e)/(G'-C) 6485 6533 G'-C 01251 01401 n/V 03692 04071 p41 nF 151664 152930 VF 4492 4068 (F-e)/(h-e) 31650 31430 (h-F)/(h-e) 6834 6856 h-e 01149 01300 n/V 03375 03758 p56 nG' 152112 153437 VG' 6630 5990 (G'-F)/(h-F) 56990 56830 (h-G')/(h-F) 4300 4316 h-F 00785 00891 n/V 02294 02561 collected indices of refraction, p71 nB 1.50770 1.51937 nC 1.50860 1.52035 ne 1.51300 1.52521 nF 1.51664 1.52930 nG' 1.52112 1.53437 nh 1.52450 1.53822 Hartmann formula constants p86 n0 1.4950214 1.5056268 Lambda_0 0.127300190 0.135600800 C 0.0063240002 0.0067280072 From dlwebb at canit.se Wed Mar 18 05:15:13 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Tue, 17 Mar 2009 21:15:13 +0100 (MET) Subject: [ATM] C1 glass In-Reply-To: <49BFFE4E.2090005@considine.net> Message-ID: On Tue, 17 Mar 2009, Matt Considine wrote: > I checked through the early issues of the Mak Circulars. They ordered > their corrector blanks from Hayward and got were looking at BSC-2. (per > Circular #1 and #7; nD 1.5170 +/- 0.001, V 64.5 +/- .4). Mirror blanks > were ordered from Corning. Sounds familiar. I certainly did not come up with BSC-2 out of thin air and know it from my efforts to learn about the Mak Club correctors. I have one of them. Please compare that Mak Circular to Roger's post to this list I mentioned earlier (23 Mar 1998). He specifically states: "The 11.25" molded blanks were made of Hayward C-1 crown glass". Does your circular have a date or mention an 11.25" molded blank? Dominic From wa4guu at verizon.net Wed Mar 18 05:16:24 2009 From: wa4guu at verizon.net (Jerry) Date: Tue, 17 Mar 2009 16:16:24 -0400 Subject: [ATM] Some improvement seen In-Reply-To: <6DAA099A9AFF4D0ABCC30E6E8EA4F366@BLAKESF.LOCAL> Message-ID: <8BC683793D5E46A391B86CA5354AD49A@D85SJB21> Ted 30 to 1 diameter to thickness. Plate glass. That is going to be very difficult. I'm tempted to say impossible to get to your intended accuracy. Astigmatism is too nice a word for the shape you have. I don't claim to know, but here are some opinions about what might be causing you problems aside from just saying "thin". It is clear that what you are doing right now is not working well. I don't think can. I wonder about the support. The pitch can give slowly under work pressure. But it will give, support will change as you work and will lag in time to shape changes of the glass from heat and flexure. The pitch support would yield under the flexing glass but not come back to shape quickly, perhaps compounding the flexure induced shape defects. The small diameter lap may be thicker and heavier than would be desired to get the work done with minimal flexure. A larger diameter lap would be spread the work more evenly over the glass, but of course it would have more friction from the increased surface area and be difficult for you to push. I believe it would work better using carpet on a flat surface to support the mirror and frequently rotate the glass 95 degrees or so. I think a larger lap will be necessary also. A tool 1.5" to 2" thick might work better than 4" or 5". There are thin mirror makers here on the list who made good thin mirrors in the past. I'm sure they may have some reasonable thoughts on how good you can expect to make a mirror that large and thin, and techniques to deal with large thin glass. Jerry -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Ted Cohen Sent: Tuesday, March 17, 2009 1:07 PM To: atm at atmlist.net Subject: Re: [ATM] Some improvement seen Re: >> I guess that this is the 23 X 3/4 inch mirror? >> What f:#? >> What size lap are you using? Yes, 23" x 3/4" floating in 3/8" layer of pitch with 1" thick aluminum plate backing. The focal ratio has crept down to about 3.9 (I was originally targeting 4.75) The tool is dental stone approximately 4"-5" thick about 11" diameter (40%-50% of mirror diameter). Worked TOT 55-gallon barrel with concrete platform. My target correction is 1/3-1/4 wave peak to valley with no turned edge. I anticipate another six months of figuring at the rate I'm going. My biggest worry at this point is the telescope mount. -----Original Message----- From: Ted Cohen As shown in the Ronchigrams http://tinyurl.com/c2eeww I still have much more work, but at least I think I'm making progress! The grating is 150 lines per inch. _______________________________________________ ATM mailing list http://www.atmlist.net/ _______________________________________________ ATM mailing list http://www.atmlist.net/ From tcohen at blakeglobal.com Wed Mar 18 06:19:46 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Tue, 17 Mar 2009 14:19:46 -0700 Subject: [ATM] Some improvement seen In-Reply-To: <8BC683793D5E46A391B86CA5354AD49A@D85SJB21> References: <6DAA099A9AFF4D0ABCC30E6E8EA4F366@BLAKESF.LOCAL> <8BC683793D5E46A391B86CA5354AD49A@D85SJB21> Message-ID: Re: >> Astigmatism is too nice a word for the shape you have. Yep, it's pretty bad! I'm not sure what the cause of the astigmatism is. It could be that I wasn't rotating the glass enough, or as mentioned, problems inherent in my setup. Ted. From rp at suttonsonline.us Wed Mar 18 06:49:40 2009 From: rp at suttonsonline.us (RP) Date: Tue, 17 Mar 2009 16:49:40 -0500 Subject: [ATM] help with an old meade dob mirror cell Message-ID: <49C01AF4.8040305@suttonsonline.us> Hello - I was recently given an older meade 8" starfinder DOB to use with my kids, and it is really a pretty nice scope. Mirror has a very nice start test when it FINALLY cools down - and thats what I need some help with. The scope has the old style meade particle board mirror cell that goes inside the tube and is about 2" thick!! This effectively seals off the back of the mirror from the outside air. 4 holes were drilled into the wood by the previous owner to help with ventilation, but even after that it still takes an hour with a house fan blowing directly on the back of the scope to bring the mirror even close to equilibrium. Is there anything I can do here? I thought about drilling lots of small diameter holes to make a honeycomb like appearance, but not sure if that will weaken the cell too much. I was going to just buy a basic aluminum cell from UO but they don't seem to sell them anymore and I do not know where else to turn. I do not have the skills or equipment to fabricate an aluminum spider. thanks RP From simo at simoivanov.com Wed Mar 18 07:01:35 2009 From: simo at simoivanov.com (simo ivanov) Date: Wed, 18 Mar 2009 07:01:35 +0900 Subject: [ATM] help with an old meade dob mirror cell In-Reply-To: <49C01AF4.8040305@suttonsonline.us> References: <49C01AF4.8040305@suttonsonline.us> Message-ID: <49C01DBF.1070007@simoivanov.com> I have a (home-made) scope that sounds like the one you do -- plain glass mirror, in a tube, glued to a cell which is bolted to a board, so it is sealed from one side. I use 4 fans from an old Dell server power supply attached to the holes so that they blow directly on the mirror surface, and except for the noise it cools down pretty fast, maybe 10-15 minutes or so. Best regards, RP wrote: > Hello - > > I was recently given an older meade 8" starfinder DOB to use with my > kids, and it is really a pretty nice scope. Mirror has a very nice start > test when it FINALLY cools down - and thats what I need some help with. > The scope has the old style meade particle board mirror cell that goes > inside the tube and is about 2" thick!! This effectively seals off the > back of the mirror from the outside air. 4 holes were drilled into the > wood by the previous owner to help with ventilation, but even after that > it still takes an hour with a house fan blowing directly on the back of > the scope to bring the mirror even close to equilibrium. Is there > anything I can do here? I thought about drilling lots of small diameter > holes to make a honeycomb like appearance, but not sure if that will > weaken the cell too much. I was going to just buy a basic aluminum cell > from UO but they don't seem to sell them anymore and I do not know where > else to turn. I do not have the skills or equipment to fabricate an > aluminum spider. > > thanks > > RP > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From rmay at nethere.com Wed Mar 18 07:03:32 2009 From: rmay at nethere.com (Bob May) Date: Tue, 17 Mar 2009 14:03:32 -0800 Subject: [ATM] Some improvement seen References: <430008.62442.qm@web54501.mail.re2.yahoo.com><730905.99337.qm@web54501.mail.re2.yahoo.com> Message-ID: <000f01c9a74c$37007620$8f78fea9@amd> I'd stay with the CeO until you get a good shap on that mirror. You've got some interesting ridges towards the outside. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Wed Mar 18 07:07:44 2009 From: rmay at nethere.com (Bob May) Date: Tue, 17 Mar 2009 14:07:44 -0800 Subject: [ATM] Some improvement seen References: <6DAA099A9AFF4D0ABCC30E6E8EA4F366@BLAKESF.LOCAL><8BC683793D5E46A391B86CA5354AD49A@D85SJB21> Message-ID: <001c01c9a74c$cd130a60$8f78fea9@amd> If you're on a machine, I'd be rotating the mirror every minute. I'd also mark the mirror so I can tell where the astig. is at for rotation angle. FWIW, on a 3/4" lens that was 13" dia., the astig would rotate (stay the same amount) in angle after a 5 minutes of machine work with a thin plaster tool. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Wed Mar 18 07:22:18 2009 From: rmay at nethere.com (Bob May) Date: Tue, 17 Mar 2009 14:22:18 -0800 Subject: [ATM] C1 glass References: Message-ID: <004501c9a74e$d6111060$8f78fea9@amd> First thing to remember anytime you're out looking for old glasses is that the amateurs usually used the cheap stuff unless they were trying to do the perfect refracter. Once you find either the 6 digit number or an individual RI for some color, it is just a matter of looking through a more modern catalog for that number and you'll have the glass. I'll note that several of the makers have changed their naming conventions over the last few years which will make things interesting again as the older glass starts coming out of the woodwork. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From simo at simoivanov.com Wed Mar 18 07:23:50 2009 From: simo at simoivanov.com (simo ivanov) Date: Wed, 18 Mar 2009 07:23:50 +0900 Subject: [ATM] help with an old meade dob mirror cell In-Reply-To: <49C02064.6030508@suttonsonline.us> References: <49C01AF4.8040305@suttonsonline.us> <49C01DBF.1070007@simoivanov.com> <49C02064.6030508@suttonsonline.us> Message-ID: <49C022F6.10007@simoivanov.com> If it blows mostly at the board, I doubt there will be a very big improvement -- it is an insulator after all. You can read more on the topic from other, more experienced people searching for "fans" like here: http://www.atmlist.net/search/namazu.cgi?query=fans&submit=Search%21&max=20&result=normal&sort=score I think my setup -- with 4 quite powerful fans -- is an overkill, but I have not bothered with more switches, as the setup works fine now (I turn the propellers off once it cools down anyway). Since you already have the holes at the back, if you have a spare fan or two, you could just tape them and see if there is any improvement. Or, maybe, you could drill one hole above the mirror, put one fan there to blow on the surface and then attach another one in the holes you already have -- one blowing, one sucking? Best, RP wrote: > thanks for the response - the 4 holes in my cell are from the back, so they > would not allow air to reach the surface of the mirror, only a small portion of > the back of the mirror - do you think that would still work? > > simo ivanov wrote: >> I have a (home-made) scope that sounds like the one you do -- plain >> glass mirror, in a tube, glued to a cell which is bolted to a board, so >> it is sealed from one side. >> >> I use 4 fans from an old Dell server power supply attached to the holes >> so that they blow directly on the mirror surface, and except for the >> noise it cools down pretty fast, maybe 10-15 minutes or so. >> From rsackett00 at yahoo.com Wed Mar 18 07:27:30 2009 From: rsackett00 at yahoo.com (Ross Sackett) Date: Tue, 17 Mar 2009 15:27:30 -0700 (PDT) Subject: [ATM] Emoticons for telescopes. In-Reply-To: <0178D1501BC94035A0F2C980C84BD44A@donaldp4> Message-ID: <154631.54938.qm@web59203.mail.re1.yahoo.com> o ( ( Schiefspiegler. --Ross --- On Tue, 3/17/09, Don D'Egidio wrote: > From: Don D'Egidio > Subject: Re: [ATM] Emoticons for telescopes. > To: "Anish Mangal" , "ATM Superheros" > Date: Tuesday, March 17, 2009, 12:19 PM > But with most of the emoticons I've seen you would tilt > your head to the left to view them. :-) > > Don > > ----- Original Message ----- > From: "Anish Mangal" > > To: "ATM Superheros" > Sent: Tuesday, March 17, 2009 1:12 PM > Subject: [ATM] Emoticons for telescopes. > > > > Hi, > > > > I was wondering if anyone's ever used emoticon > text to describe telescopes > > ;) > > > > I came up with a few (assuming target FOV at right) > > > > Newtonian reflector : ( \ > > Simple refractor : o O > > Cassegrain : ( | > > Mak-Cass : ( ( > > > > > > Maybe these can be a part of ATM lingo... > > > > Cheers! > > Anish Mangal > > _______________________________________________ > > ATM mailing list http://www.atmlist.net/ > > > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From matt at considine.net Wed Mar 18 08:15:17 2009 From: matt at considine.net (Matt Considine) Date: Tue, 17 Mar 2009 19:15:17 -0400 Subject: [ATM] C1 glass Message-ID: <49C02F05.4020203@considine.net> Quoting from page 1 of the first issue of the Maksutov Circulars (dated 2/14/1957) : "The Glass. With regard to the corrector blanks, I have contacted several manufacturers, none of whom have been other than thoroughly reputable firms who will stand behind their product. Estimates have varied to a surprising extent and much the best has been from the Hayward Scientific Glass Corp. of Whittier, California, a firm which has a very reliable name in glass manufacture. The particulars are as follow[sic]: Dia. R1 R2 Thickness Weight Price 10 1/4" 15 1/4" 16 1/4" 1 1/4" 9.1 lbs. $51.75 11 1/4" 17" 18 3/8" 1 3/8" 13 $72.50 Both prices are all charges included, individually packaged and deliverd to the door of the buyer, assuming that he is within the 8th postal district. Delivery 45-60 days from receipt of the order on the 10 1/4", and 60-75 days on the 11 1/4". Further particulars are : BSC-2 ND 1.5170 +/- .001 V 64.5 +/- .4 Quality Grade A as defined JAN G 174 Anneal Fine annealed Bubbles Virtually free from bubbles Edge Molded finish" In issue #7 (dated 5/15/1957) it is stated "the main body of the orders went forward to Haywards and Corning on May 2nd, and the last gasp people will be going in today." In issue #17 (9/19/1957) there is mention of Gregory's design adapted for a 6" scope. An Ed Lindberg coordinated this effort and the desciption of the glass was "The blanks are 6.65" dia., approx. 3/4" thick, BSC-2, and are priced at $26.00 [...]". In issue #25 (dated 12/15/1957) there is a discussion of a 6" "branch" of the Mak Club, noting that "an order for 20 blanks has already been sent in to Haywards [...]" Finally, in issue #42 (dated 9/20/1958, regarding the start of the club) it is stated "The order was given to the Hayward Scientific Glass Corporation in 1957 and has since been filled satisfactorily. Haywards still supply the correctors for individual orders, and largely because of the success of the Club, have begun manufacturing corrector blanks in several sizes." So from all this, I gather that the glass used for the correctors was in fact BSC-2 and was from Haywards. Matt From astroguy at nas.com Wed Mar 18 09:40:57 2009 From: astroguy at nas.com (kreig) Date: Tue, 17 Mar 2009 17:40:57 -0700 Subject: [ATM] Emoticons for telescopes References: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> Message-ID: <001901c9a762$376158d0$bd2aff04@LILBERT> The only real telescope........................... )(() ----- Original Message ----- From: "Anish Mangal" To: "ATM Superheros" Sent: Tuesday, March 17, 2009 10:12 AM Subject: [ATM] Emoticons for telescopes. > Hi, > > I was wondering if anyone's ever used emoticon text to describe telescopes > ;) > > I came up with a few (assuming target FOV at right) > > Newtonian reflector : ( \ > Simple refractor : o O > Cassegrain : ( | > Mak-Cass : ( ( > > > Maybe these can be a part of ATM lingo... > > Cheers! > Anish Mangal > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > > > -- > Internal Virus Database is out-of-date. > Checked by AVG Free Edition. > Version: 7.1.413 / Virus Database: 268.18.23/740 - Release Date: 3/30/2007 > > From shane at ct-astronomer.com Wed Mar 18 10:02:22 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Tue, 17 Mar 2009 21:02:22 -0400 Subject: [ATM] Emoticons for telescopes In-Reply-To: <001901c9a762$376158d0$bd2aff04@LILBERT> References: <47eee29a0903171012j2d23ded8s83e9a3dbdc5ffab4@mail.gmail.com> <001901c9a762$376158d0$bd2aff04@LILBERT> Message-ID: Hey, if you want to polish 6 surfaces for a 4" scope.... then be my guest :) Good one. These are funny. Ok.. how about: focuser: |o| 2" focuser |O| On Mar 17, 2009, at 8:40 PM, kreig wrote: > The only real telescope........................... )(() > > > > > ----- Original Message ----- From: "Anish Mangal" > > To: "ATM Superheros" > Sent: Tuesday, March 17, 2009 10:12 AM > Subject: [ATM] Emoticons for telescopes. > > >> Hi, >> >> I was wondering if anyone's ever used emoticon text to describe >> telescopes >> ;) >> >> I came up with a few (assuming target FOV at right) >> >> Newtonian reflector : ( \ >> Simple refractor : o O >> Cassegrain : ( | >> Mak-Cass : ( ( >> >> >> Maybe these can be a part of ATM lingo... >> >> Cheers! >> Anish Mangal >> _______________________________________________ >> ATM mailing list http://www.atmlist.net/ >> >> >> >> -- >> Internal Virus Database is out-of-date. >> Checked by AVG Free Edition. >> Version: 7.1.413 / Virus Database: 268.18.23/740 - Release Date: >> 3/30/2007 >> > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From holmmarkd at gmail.com Wed Mar 18 10:19:14 2009 From: holmmarkd at gmail.com (Mark Holm) Date: Tue, 17 Mar 2009 21:19:14 -0400 Subject: [ATM] help with an old meade dob mirror cell In-Reply-To: <49C01AF4.8040305@suttonsonline.us> References: <49C01AF4.8040305@suttonsonline.us> Message-ID: <49C04C12.9080400@gmail.com> How are your wood working skills? If you start with a reasonably good grade of 3/4 inch plywood, you can make a cell with pretty substantial cutouts and it will still be plenty stiff. If you don't want to use a fan, go for a smaller number of larger cutouts rather than a larger number of smaller cutouts. For instance, you could have a two board cell with the two boards cut away to make equilateral triangles, with rounded corners to fit the tube and the mirror. You can even round into the sides of the triangles some to make more open area. Remember, Plop says, for a three point support, the points (pads really) should be on the 40% diameter of the mirror. -- Mark Holm markholm at verizon.net holmmarkd at gmail.com From dlwebb at canit.se Wed Mar 18 19:25:05 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Wed, 18 Mar 2009 11:25:05 +0100 (MET) Subject: [ATM] C1 glass In-Reply-To: <49C03076.60905@considine.net> Message-ID: On Tue, 17 Mar 2009, Matt Considine wrote: > By the way, do you have one of the original glass sets? If so, can you > share the history of it?? > Matt I am not aware of a glass set. I bought one 11.25" meniscus from Chabot Observatory telescope workshop in Oakland, California, USA about 10 years ago. I got a suggestion at the time of purchase that it was likely BSC-2 and would closely conform to BK-7 specifications. However, the email from Roger at S&T explicitly stated it was C-1. The Norman A Burts article in Dec 1957 S&T describes the design of the 11.25" scope for C-1, but goes on to state that for amateurs the more common BSC-2 could be used. It does not state any price difference between C-1 and BSC-2 or which was ordered by the Mak Club. Both glass types were manufactured by Hayward Glass Corp (aka Hayward Scientific) in Whittier, California. I could guess mine is in fact BSC-2. Given the above, it is clear why there is confusion. I would accept the Mak Club circular as more direct from the source. If that says BSC-2, that is what we should accept as most factually correct. This whole matters gets complicated because I earlier did not have access to the Burts article. I attempted to design a scope around the meniscus blank R1 and R2, assuming this must approximate the intended design. I never found an acceptable design using the 12" F/5 primary I have. At some point, Mauritz Andersson here in Sweden who sometime posts to this list, offered some help with Oslo software. A design was reached using a rather long F/5 primary mirror that called for removing a lot of glass from the corrector to make it much thinner. While spot diagram was impressive, it undermined the purpose of the corrector. The result was a scope with a very long tube. In the past ~2 years, I located the Dec 1957 S&T article by Burts and punched in the prescription using C-1 in metric units: http://www.canit.se/~dlwebb/catadioptric/320maksutov/320maksutov.html I exclude the secondary conic for now, starting with an all spherical system. The spot diagram was still hopeless. I am thus far unable to obtain any suitable design, so the meniscus blank has remained a blank, with only some rough grinding only to remove surface patterns from the mold. Adding a conic to the Cass secondary can a help slightly, but does not solve the problem that this system is very far from diffraction limited. Changing meniscus glass type only marginally changes the ray trace. Slightly aspherizing the meniscus first surface helps only slightly. Hence, I asked about things like field curvature, etc because I want to be certain I have not over-looked anything before truly concluding there is a problem with the published design in Dec 1957 S&T article by Norman A Burts. I now expect to use a considerably faster primary, around F/3 to F/4. Cass secondary will then give amplification around 3-4. An exact prescription yielding acceptable ray trace has yet to materialize. Dominic From matt at considine.net Wed Mar 18 22:43:39 2009 From: matt at considine.net (Matt Considine) Date: Wed, 18 Mar 2009 09:43:39 -0400 Subject: [ATM] C1 glass Message-ID: <49C0FA8B.90709@considine.net> Hi, Well, I'm a bit puzzled. I don't have the 1957 issue of S&T. But an August 1957 issue (#15) of the Mak Circulars has a design by "B. A. Norman" of Canada for a f/4.2-f/20.24 Mak-Cass-Newt using an 11.25" corrector explicitly stated to be of BSC-2. Converting the numbers in that issue to metric, I get exactly the same numbers (allowing for rounding in the third decimal place) as presented in Dominic's table. Matt From matt at considine.net Wed Mar 18 23:38:20 2009 From: matt at considine.net (Matt Considine) Date: Wed, 18 Mar 2009 10:38:20 -0400 Subject: [ATM] C1 glass Message-ID: <49C1075C.4060200@considine.net> Dominic, did you place any aspherizing on the secondary when you modeled it? For what it's worth, in Mak Circular #30, there was a design published for another Cass- Newt Mak, designed by Raab and Gregory. I assume it is reprinted in "ATMT" but here are the numbers Clear aperture 11" Mirror Dia 12 1/4" Corrector : R1 -16.754 d1 1.266 R2 -17.446 Spacing to primary 47.45 R3 (primary) -90.555 Spacing from primary to secondary -37.886 R4 (secondary, convex) -19.953 efl 44.13 prime focus = f/4 eccentricity of R4 1.4 A 3" Newtonian diagonal placed in same position as Cass secondary gives 100% illumination over a .75" field Hope this helps, Matt From dlwebb at canit.se Wed Mar 18 23:44:30 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Wed, 18 Mar 2009 15:44:30 +0100 (MET) Subject: [ATM] C1 glass In-Reply-To: <49C0FA8B.90709@considine.net> Message-ID: On Wed, 18 Mar 2009, Matt Considine wrote: > Hi, > Well, I'm a bit puzzled. I don't have the 1957 issue of S&T. But an > August 1957 issue (#15) of the Mak Circulars has a design by "B. A. > Norman" of Canada for a f/4.2-f/20.24 Mak-Cass-Newt using an 11.25" > corrector explicitly stated to be of BSC-2. > > Converting the numbers in that issue to metric, I get exactly the same > numbers (allowing for rounding in the third decimal place) as presented > in Dominic's table. > > Matt Thanks Matt! So let us then say the prescription I posted correctly states Norman A Burts' 11.25" diameter corrector design if applied to Hayward Glass Corp BSC2 meniscus as indicated in the legend in my picture of the actual glass: http://www.canit.se/~dlwebb/catadioptric/320maksutov/320maksutov.html With either glass, the Burt's design in S&T calls for the Cass secondary to be hyperbolic. Using the equations offered in the Dec 1957 S&T article for BSC2, I get eccentricity (e) of 1.518995. Conic constent is related by k = -e^2, giving -2.307346. The relative merits of spherical vs hyperbolic secondary could be discussed. For my Oslo tests, I have used BK7 and other glass in the software catalog database; it does not have Hayward BSC2 or C1. I have not yet learned to create a custom glass in Oslo. Following some optimization I basically get similar results with the different glass I have tried so far. Dominic From rflrs at rcn.com Thu Mar 19 00:16:51 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Wed, 18 Mar 2009 10:16:51 -0500 Subject: [ATM] C1 glass In-Reply-To: References: Message-ID: <49C11063.10500@rcn.com> Dominic-Luc Webb wrote: > > > > For my Oslo tests, I have used BK7 and other glass in the > software catalog database; it does not have Hayward BSC2 > or C1. I have not yet learned to create a custom glass in Oslo. > Following some optimization I basically get similar results > with the different glass I have tried so far. You might use H_BSC2. In my [older] version of OSLO, it's already in the obsolete catalog, though. From dlwebb at canit.se Thu Mar 19 00:18:46 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Wed, 18 Mar 2009 16:18:46 +0100 (MET) Subject: [ATM] C1 glass In-Reply-To: <49C1075C.4060200@considine.net> Message-ID: On Wed, 18 Mar 2009, Matt Considine wrote: > Dominic, did you place any aspherizing on the secondary when you modeled it? I have made many models. These included hyperbolic secondary and mildly aspherized corrector first surface (conic ~-0.0001) with reduced corrector thickness. I also tried changing glass types. Again, I have been using Oslo, which does not have BSC2 in the catalog database. I chose glass that approximates BSC2. Ray traces come out about same after some optimizations, but no impressive ray trace so far that makes me feel enthusiastic about building it. Dominic From vla at copper.net Thu Mar 19 00:30:17 2009 From: vla at copper.net (vladimir sacek) Date: Wed, 18 Mar 2009 11:30:17 -0400 Subject: [ATM] C1 glass References: Message-ID: <002b01c9a7de$7203cdc0$a159f804@Handsome> Dominic, >I now expect to use a considerably > faster primary, around F/3 to F/4. Cass secondary > will then give amplification around 3-4. An exact > prescription yielding acceptable ray trace has yet to > materialize. Getting good approximation of design parameters is pretty much described in the Mak section on my site, but it is probably a bit time consuming to dig it out. Here's all it takes to determine MCT system parameters very close to its optimized version: R1~R(1-2t-0.01F){[T(n+2)(n-1)^2]/2(n^3)(1-s)R}^0.25 R2=R1-{[1-(1/n^2)]T/0.97} where R1 and R2 are the front and rear corrector radius, respectively, R is the primary mirror r.o.c., "n" is the glass refractive, T the corrector center thickness, and s=[(m-1)(m+1)^2]/m^3, "m" being the secondary magnification. Note that R, R1 and R2 are all numerically negative. Coma and astigmatism are inherently low in typical MCT systems, due to combined aberrations of the corrector and secondary offsetting that of the primary. Coma can be cancelled, but some residual astigmatism remains. The only benefit of aspherizing is aspherizing the primary in larger systems with the primary faster than ~f/3. It allows for weaker corrector, which in turn lowers the minimum residual spherical (i.e. balanced higher-order). The above system assumes corrector close to the secondary (i.e. secondary attached to the rear side of corrector). Moving corrector somewhat farther out to make room for a diagonal flat doesn't produce significant effect. Vla -------------------------------------------------------------------------------- Internal Virus Database is out of date. Checked by AVG - www.avg.com Version: 8.0.237 / Virus Database: 270.11.9/1992 - Release Date: 03/09/09 19:20:00 From dlwebb at canit.se Thu Mar 19 00:35:16 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Wed, 18 Mar 2009 16:35:16 +0100 (MET) Subject: [ATM] C1 glass In-Reply-To: <49C11063.10500@rcn.com> Message-ID: We have drifted pretty far from original post. Maybe subject on this thread should change. Could I suggest "BSC2 glass"... Dominic From dlwebb at canit.se Thu Mar 19 00:38:38 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Wed, 18 Mar 2009 16:38:38 +0100 (MET) Subject: [ATM] BSC2 glass Message-ID: Any links/info on how to precisely measure glass optical parameters like refractive index? Values to be measured on original 11.25" Mak Club Corrector for purpose of simulating exact prescription in software. Dominic From melockwo at uiuc.edu Thu Mar 19 01:47:02 2009 From: melockwo at uiuc.edu (Mike Lockwood) Date: Wed, 18 Mar 2009 10:47:02 -0600 Subject: [ATM] Impossible? I think not. In-Reply-To: References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> Message-ID: <49C12586.1010301@uiuc.edu> Hi, Ted Cohen wrote: > A 48-inch F3 with any glass thickness is impossible for an amateur. > By hand, it would probably take about 10 years to complete just the > mirror. Furthermore, the glass and the tool would both be too heavy > to lift. The glass would be difficult to mount, and would require a > huge engineering job to design the appropriate telescope tube and > mounting. After 10 years of work, you might find that the figure on > the glass is so bad, that it is only equivalent to the power of a > 6-inch mirror. The cost, complexity and difficulty of the project > increases exponentially with the size of the mirror. Also, an F/3 > parabola is very difficult to figure accurately without expensive > equipment. You're better off sticking to what everyone else is doing > in the 8"-inch F/6 to F/10 range, which can be achieved relatively > quickly and accurately. Interesting - at first I thought that had to be sarcasm to be so negative, but then I realized it was to be taken literally. It is one thing to politely inform a fellow list member of the difficulties of a project, but it is quite another to all but guarantee failure. Dave has been pushing the envelope for a while now and sharing his successes and failures with the list. I think you owe him an apology. I found that post ironic (I could have said hypocritical) after I read that you were working on this: Ted Cohen wrote: > 23" x 3/4" floating in 3/8" layer of pitch with 1" thick > aluminum plate backing. The focal ratio has crept down to about 3.9 > (I was originally targeting 4.75) The tool is dental stone > approximately 4"-5" thick about 11" diameter (40%-50% of mirror > diameter). Worked TOT 55-gallon barrel with concrete platform. My > target correction is 1/3-1/4 wave peak to valley with no turned edge. > I anticipate another six months of figuring at the rate I'm going. My > biggest worry at this point is the telescope mount. Personally I would prefer a 48" F/3 from a stable substrate over the sandwich any day. I have a friend who is building a 48" F/4, and it's not a huge engineering job, by the way. However, I will not doom your project to failure - I encourage you to persevere. I will simply offer some thoughts and advice. I think your biggest issue is the aluminum backing changing dimension with fluctuating temperature. I have seen what aluminum bonded to glass can do, and it can be a big problem. That might account for the serious astigmatism you are seeing. If you can keep it at a constant temperature while you work and test, you might see improved results. OK, point made. On a lighter note.... Anish wrote: > I was wondering if anyone's ever used emoticon text to describe telescopes > I came up with a few (assuming target FOV at right) > Newtonian reflector : ( \ I like it, but the obstruction on that Newtonian appears to be >=100%, so I'd suggest this: / ( / \ There might be a bit of a central depression in that mirror, but at least some light is getting to the focal plane. It's bigger than the refractors, too. :o Mike Lockwood Lockwood Custom Optics From vla at copper.net Thu Mar 19 00:57:56 2009 From: vla at copper.net (vladimir sacek) Date: Wed, 18 Mar 2009 11:57:56 -0400 Subject: [ATM] C1 glass References: <002b01c9a7de$7203cdc0$a159f804@Handsome> Message-ID: <001201c9a7e2$4f459ee0$725af804@Handsome> Here's all it takes to determine MCT > system parameters very close to its optimized version: > > R1~R(1-2t-0.01F){[T(n+2)(n-1)^2]/2(n^3)(1-s)R}^0.25 > R2=R1-{[1-(1/n^2)]T/0.97} > > where R1 and R2 are the front and rear corrector radius, respectively, > R is the primary mirror r.o.c., "n" is the glass refractive, T the > corrector > center thickness, and s=[(m-1)(m+1)^2]/m^3, "m" being the secondary > magnification. Note that R, R1 and R2 are all numerically negative. > Dropped t=T/R Vla From rflrs at rcn.com Thu Mar 19 01:15:42 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Wed, 18 Mar 2009 11:15:42 -0500 Subject: [ATM] C1 glass In-Reply-To: References: Message-ID: <49C11E2E.9030607@rcn.com> Dominic-Luc Webb wrote: > > With either glass, the Burt's design in S&T calls for the Cass > secondary to be hyperbolic. Using the equations offered in the > Dec 1957 S&T article for BSC2, I get eccentricity (e) of 1.518995. > Conic constent is related by k = -e^2, giving -2.307346. The > relative merits of spherical vs hyperbolic secondary could be > discussed. > > For my Oslo tests, I have used BK7 and other glass in the > software catalog database; it does not have Hayward BSC2 > or C1. I have not yet learned to create a custom glass in Oslo. > Following some optimization I basically get similar results > with the different glass I have tried so far. For that corrector, and assuming some of the geometry constraints (the thickness pickups), to me, OSLO seems to recommend a stronger primary and adding a 6th order correction (about 1/4 micron) to an oblate secondary: SRF RADIUS THICKNESS APERTURE RADIUS GLASS SPE NOTE OBJ -- 1.0000e+20 1.7453e+17 AIR AST -- 23.08799 S 139.70000 AS AIR 2 -434.19000 29.34000 139.74030 S H_BSC2 C 3 -451.08010 V 1119.15422 V 142.99798 S AIR 4 -2096.73841 V -865.15422 P 147.75297 S REFLECT 5 -495.15779 V 1119.15422 P 29.49740 S REFLECT * 6 -- -- 9.86317 S AIR IMS -- -- 9.86317 S *CONIC AND POLYNOMIAL ASPHERIC DATA SRF CC AD AE AF AG 5 1.0185e+00 -- 4.0885e-13 -- -- *PICKUPS 4 THM 3 254.00000 1.00000 5 THM 4 254.00000 1.00000 From astroguy at nas.com Thu Mar 19 01:19:48 2009 From: astroguy at nas.com (astroguy at nas.com) Date: Wed, 18 Mar 2009 12:19:48 -0400 Subject: [ATM] Impossible? - larger refractor Message-ID: <380-220093318161948267@M2W034.mail2web.com> Ok, here is a larger refractor, take "that" reflector guys!!!! \ / /\ \ / / \ l l l l / \ \ / / \ \/ Kreig _________________________________________________________________ "There might be a bit of a central depression in that mirror, but at least some light is getting to the focal plane. It's bigger than the refractors, too. :o " Original Message: ----------------- From: Mike Lockwood melockwo at uiuc.edu Date: Wed, 18 Mar 2009 10:47:02 -0600 To: atm at atmlist.net Subject: [ATM] Impossible? I think not. Hi, Ted Cohen wrote: > A 48-inch F3 with any glass thickness is impossible for an amateur. > By hand, it would probably take about 10 years to complete just the > mirror. Furthermore, the glass and the tool would both be too heavy > to lift. The glass would be difficult to mount, and would require a > huge engineering job to design the appropriate telescope tube and > mounting. After 10 years of work, you might find that the figure on > the glass is so bad, that it is only equivalent to the power of a > 6-inch mirror. The cost, complexity and difficulty of the project > increases exponentially with the size of the mirror. Also, an F/3 > parabola is very difficult to figure accurately without expensive > equipment. You're better off sticking to what everyone else is doing > in the 8"-inch F/6 to F/10 range, which can be achieved relatively > quickly and accurately. Interesting - at first I thought that had to be sarcasm to be so negative, but then I realized it was to be taken literally. It is one thing to politely inform a fellow list member of the difficulties of a project, but it is quite another to all but guarantee failure. Dave has been pushing the envelope for a while now and sharing his successes and failures with the list. I think you owe him an apology. I found that post ironic (I could have said hypocritical) after I read that you were working on this: Ted Cohen wrote: > 23" x 3/4" floating in 3/8" layer of pitch with 1" thick > aluminum plate backing. The focal ratio has crept down to about 3.9 > (I was originally targeting 4.75) The tool is dental stone > approximately 4"-5" thick about 11" diameter (40%-50% of mirror > diameter). Worked TOT 55-gallon barrel with concrete platform. My > target correction is 1/3-1/4 wave peak to valley with no turned edge. > I anticipate another six months of figuring at the rate I'm going. My > biggest worry at this point is the telescope mount. Personally I would prefer a 48" F/3 from a stable substrate over the sandwich any day. I have a friend who is building a 48" F/4, and it's not a huge engineering job, by the way. However, I will not doom your project to failure - I encourage you to persevere. I will simply offer some thoughts and advice. I think your biggest issue is the aluminum backing changing dimension with fluctuating temperature. I have seen what aluminum bonded to glass can do, and it can be a big problem. That might account for the serious astigmatism you are seeing. If you can keep it at a constant temperature while you work and test, you might see improved results. OK, point made. On a lighter note.... Anish wrote: > I was wondering if anyone's ever used emoticon text to describe telescopes > I came up with a few (assuming target FOV at right) > Newtonian reflector : ( \ I like it, but the obstruction on that Newtonian appears to be >=100%, so I'd suggest this: / ( / \ There might be a bit of a central depression in that mirror, but at least some light is getting to the focal plane. It's bigger than the refractors, too. :o Mike Lockwood Lockwood Custom Optics _______________________________________________ ATM mailing list http://www.atmlist.net/ -------------------------------------------------------------------- mail2web.com ? What can On Demand Business Solutions do for you? http://link.mail2web.com/Business/SharePoint From mbartels at bbastrodesigns.com Thu Mar 19 01:43:43 2009 From: mbartels at bbastrodesigns.com (mbartels at bbastrodesigns.com) Date: Wed, 18 Mar 2009 10:43:43 -0600 Subject: [ATM] cost of test equipment, was Re: Impossible? I think not. In-Reply-To: <49C12586.1010301@uiuc.edu> References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> <49C12586.1010301@uiuc.edu> Message-ID: <20090318104343.qd5wrvrndc8o08gs@bbastrodesigns.com> >>> Ted Cohen wrote: >>> Also, an F/3 parabola is very difficult to figure accurately >>> without expensive equipment. I figured my 13 inch f/3.0 using a Ronchi tester and the star test. Total cost of test equipment was about $20. Mel Bartels From tcohen at blakeglobal.com Thu Mar 19 02:37:47 2009 From: tcohen at blakeglobal.com (Ted Cohen) Date: Wed, 18 Mar 2009 10:37:47 -0700 Subject: [ATM] Impossible? I think not. In-Reply-To: <49C12586.1010301@uiuc.edu> References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> <49C12586.1010301@uiuc.edu> Message-ID: Ted Cohen Re: >> Dave has >> been pushing the envelope for a while now and sharing his successes and >> failures with the list. I think you owe him an apology. I apologize Dave. Mike is right. I shouldn't have been so disparaging. In hindsight it was rude of me to comment like that, especially since I'm a newbie and haven't the experience of the other atmers on this list. I wish you speedy success in your 48" inch project. You probably have more experience than I, thus making the desired outcome far more likely than that which I am attempting. I also apologize to the whole list for this indiscretion. Ted. -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Mike Lockwood Sent: Wednesday, March 18, 2009 9:47 AM To: atm at atmlist.net Subject: [ATM] Impossible? I think not. Hi, Ted Cohen wrote: > A 48-inch F3 with any glass thickness is impossible for an amateur. > By hand, it would probably take about 10 years to complete just the > mirror. Furthermore, the glass and the tool would both be too heavy > to lift. The glass would be difficult to mount, and would require a > huge engineering job to design the appropriate telescope tube and > mounting. After 10 years of work, you might find that the figure on > the glass is so bad, that it is only equivalent to the power of a > 6-inch mirror. The cost, complexity and difficulty of the project > increases exponentially with the size of the mirror. Also, an F/3 > parabola is very difficult to figure accurately without expensive > equipment. You're better off sticking to what everyone else is doing > in the 8"-inch F/6 to F/10 range, which can be achieved relatively > quickly and accurately. Interesting - at first I thought that had to be sarcasm to be so negative, but then I realized it was to be taken literally. It is one thing to politely inform a fellow list member of the difficulties of a project, but it is quite another to all but guarantee failure. Dave has been pushing the envelope for a while now and sharing his successes and failures with the list. I think you owe him an apology. I found that post ironic (I could have said hypocritical) after I read that you were working on this: Ted Cohen wrote: > 23" x 3/4" floating in 3/8" layer of pitch with 1" thick > aluminum plate backing. The focal ratio has crept down to about 3.9 > (I was originally targeting 4.75) The tool is dental stone > approximately 4"-5" thick about 11" diameter (40%-50% of mirror > diameter). Worked TOT 55-gallon barrel with concrete platform. My > target correction is 1/3-1/4 wave peak to valley with no turned edge. > I anticipate another six months of figuring at the rate I'm going. My > biggest worry at this point is the telescope mount. Personally I would prefer a 48" F/3 from a stable substrate over the sandwich any day. I have a friend who is building a 48" F/4, and it's not a huge engineering job, by the way. However, I will not doom your project to failure - I encourage you to persevere. I will simply offer some thoughts and advice. I think your biggest issue is the aluminum backing changing dimension with fluctuating temperature. I have seen what aluminum bonded to glass can do, and it can be a big problem. That might account for the serious astigmatism you are seeing. If you can keep it at a constant temperature while you work and test, you might see improved results. OK, point made. On a lighter note.... Anish wrote: > I was wondering if anyone's ever used emoticon text to describe telescopes > I came up with a few (assuming target FOV at right) > Newtonian reflector : ( \ I like it, but the obstruction on that Newtonian appears to be >=100%, so I'd suggest this: / ( / \ There might be a bit of a central depression in that mirror, but at least some light is getting to the focal plane. It's bigger than the refractors, too. :o Mike Lockwood Lockwood Custom Optics _______________________________________________ ATM mailing list http://www.atmlist.net/ From rflrs at rcn.com Thu Mar 19 02:36:55 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Wed, 18 Mar 2009 12:36:55 -0500 Subject: [ATM] BSC2 glass In-Reply-To: References: Message-ID: <49C13137.8020500@rcn.com> Dominic-Luc Webb wrote: > Any links/info on how to precisely measure glass optical > parameters like refractive index? Values to be > measured on original 11.25" Mak Club Corrector > for purpose of simulating exact prescription in > software. If the first order (lens strength) is used, wouldn't that be kind of inaccurate with such a weak lens? From mbartels at bbastrodesigns.com Thu Mar 19 03:17:15 2009 From: mbartels at bbastrodesigns.com (mbartels at bbastrodesigns.com) Date: Wed, 18 Mar 2009 12:17:15 -0600 Subject: [ATM] judging impossible from plausible, was Re: Impossible? I think not. In-Reply-To: References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> <49C12586.1010301@uiuc.edu> Message-ID: <20090318121715.khnqkxvhk4880c4s@bbastrodesigns.com> > I apologize Dave. Mike is right. I shouldn't have been so disparaging. In > hindsight it was rude of me to comment like that, especially since I'm a > newbie and haven't the experience of the other atmers on this list. I wish > you speedy success in your 48" inch project. You probably have more > experience than I, thus making the desired outcome far more likely than that > which I am attempting. I also apologize to the whole list for this > indiscretion. It's easy to type out a few words and hit the send button without considering how others will read it. I know because I've done my share! Perhaps the basis for you 'taking exception' is that instant judgement that we all make when facing something new or unusual. It appears to be some sort of analog emotional computation that goes on in our head. A 48" f/3 from 1/4" thick plate glass fused to foam does at first glance seem to exceed the tipping point of reasonableness. After all, the original post did little to explain the serious background of the project and the forces that are leading to this type of experiment. My approach is to learn the principles. To do that I need the theory along with the practice. Not easy for me - it can take a lot of time. Then I can judge better the efficacy. Even so, there's that initial resistance to something new which devalues what I know. I face this in software on a daily basis because technologies and processes change at a dizzying and challenging rate. The reason I mention all this now is to help amateurs deal with the multitude of mirror making approaches. Beginning amateurs often comment on how contradictory advice seems. For me, I judge approaches on principles, then if the approaches help us achieve a successful outcome. For beginners it is best to pick a popular and well thought of approach and stick to it, turning a deaf ear to alternatives. As one gains experience, then the contradictions and complications can be slowly introduced. Mel Bartels From shane at ct-astronomer.com Thu Mar 19 03:30:18 2009 From: shane at ct-astronomer.com (Shane LaPierre) Date: Wed, 18 Mar 2009 14:30:18 -0400 Subject: [ATM] judging impossible from plausible, was Re: Impossible? I think not. In-Reply-To: <20090318121715.khnqkxvhk4880c4s@bbastrodesigns.com> References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org> <49C12586.1010301@uiuc.edu> <20090318121715.khnqkxvhk4880c4s@bbastrodesigns.com> Message-ID: On this thread in particular there are a lot of ideas being tried. That's what makes this forum so great... contemplating "impossible" ideas because it was shared by somebody else. Personally if there are plausible ways to come up with 48" mirrors of good quality I am for the easiest way to produce it. I hope this turns into something. Best wishes, Shane LaPierre On Mar 18, 2009, at 2:17 PM, mbartels at bbastrodesigns.com wrote: > > > It's easy to type out a few words and hit the send button without > considering how others will read it. I know because I've done my > share! > > Perhaps the basis for you 'taking exception' is that instant > judgement that we all make when facing something new or unusual. It > appears to be some sort of analog emotional computation that goes on > in our head. A 48" f/3 from 1/4" thick plate glass fused to foam > does at first glance seem to exceed the tipping point of > reasonableness. After all, the original post did little to explain > the serious background of the project and the forces that are > leading to this type of experiment. > > My approach is to learn the principles. To do that I need the > theory along with the practice. Not easy for me - it can take a lot > of time. Then I can judge better the efficacy. Even so, there's > that initial resistance to something new which devalues what I know. > > I face this in software on a daily basis because technologies and > processes change at a dizzying and challenging rate. > > The reason I mention all this now is to help amateurs deal with the > multitude of mirror making approaches. Beginning amateurs often > comment on how contradictory advice seems. > > For me, I judge approaches on principles, then if the approaches > help us achieve a successful outcome. For beginners it is best to > pick a popular and well thought of approach and stick to it, turning > a deaf ear to alternatives. As one gains experience, then the > contradictions and complications can be slowly introduced. > > Mel Bartels > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From dlwebb at canit.se Thu Mar 19 03:49:26 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Wed, 18 Mar 2009 19:49:26 +0100 (MET) Subject: [ATM] judging impossible from plausible, was Re: Impossible? I think not. In-Reply-To: Message-ID: Reflecting back on the original 1960's Star Trek TV series, consider how many of those insane devices, etc were fabricated outright from people who had no particular science background. Many of these things ultimately became real, partly because people saw them on TV and reckoned they needed to be invented - somehow! Dominic From rflrs at rcn.com Thu Mar 19 03:55:28 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Wed, 18 Mar 2009 13:55:28 -0500 Subject: [ATM] C1 glass In-Reply-To: <49C11E2E.9030607@rcn.com> References: <49C11E2E.9030607@rcn.com> Message-ID: <49C143A0.5090505@rcn.com> Richard F.L.R. Snashall wrote: > > For that corrector, and assuming some of the geometry > constraints (the thickness pickups), to me, OSLO seems > to recommend a stronger primary and adding a 6th order > correction (about 1/4 micron) to an oblate secondary: Even when forced to use the complete Newt configuration, I still get roughly the same 6th order correction as a better solution (with about +390 micron change in back focus from the given design): *CONIC AND POLYNOMIAL ASPHERIC DATA SRF CC AD AE AF AG 5 -9.8456e-01 -- 4.3315e-13 -- -- From wa4guu at verizon.net Thu Mar 19 04:09:33 2009 From: wa4guu at verizon.net (Jerry) Date: Wed, 18 Mar 2009 15:09:33 -0400 Subject: [ATM] Impossible? I think not. In-Reply-To: <49C12586.1010301@uiuc.edu> Message-ID: <84C0553C1EB54BE388CFB931F9CA5357@D85SJB21> A bit of overkill here. One could say that you owe Ted an apology for alleging some sort of malice on his part. It seems that Ted said what he believed to be true. There may be factual inaccuracies in his comments but I don't see any clue that he was being insincere. I don't see rudeness. If Ted believes that Dave is tilting at windmills it is kind of him to say so. Dave has the option to weigh the validity of Ted's comments along with any other comments he may receive. He can weight the value by logic and source and whatever else he wishes. Perhaps Dave likes that he is attempting what seems impossible to others. It could be that he is not offended at all. Dave seemed to handle the negativity well enough in his reply. -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of Mike Lockwood Sent: Wednesday, March 18, 2009 12:47 PM To: atm at atmlist.net Subject: [ATM] Impossible? I think not. Hi, Ted Cohen wrote: > A 48-inch F3 with any glass thickness is impossible for an amateur. > By hand, it would probably take about 10 years to complete just the > mirror. Furthermore, the glass and the tool would both be too heavy > to lift. The glass would be difficult to mount, and would require a > huge engineering job to design the appropriate telescope tube and > mounting. After 10 years of work, you might find that the figure on > the glass is so bad, that it is only equivalent to the power of a > 6-inch mirror. The cost, complexity and difficulty of the project > increases exponentially with the size of the mirror. Also, an F/3 > parabola is very difficult to figure accurately without expensive > equipment. You're better off sticking to what everyone else is doing > in the 8"-inch F/6 to F/10 range, which can be achieved relatively > quickly and accurately. Interesting - at first I thought that had to be sarcasm to be so negative, but then I realized it was to be taken literally. It is one thing to politely inform a fellow list member of the difficulties of a project, but it is quite another to all but guarantee failure. Dave has been pushing the envelope for a while now and sharing his successes and failures with the list. I think you owe him an apology. I found that post ironic (I could have said hypocritical) after I read that you were working on this: Ted Cohen wrote: > 23" x 3/4" floating in 3/8" layer of pitch with 1" thick > aluminum plate backing. The focal ratio has crept down to about 3.9 > (I was originally targeting 4.75) The tool is dental stone > approximately 4"-5" thick about 11" diameter (40%-50% of mirror > diameter). Worked TOT 55-gallon barrel with concrete platform. My > target correction is 1/3-1/4 wave peak to valley with no turned edge. > I anticipate another six months of figuring at the rate I'm going. My > biggest worry at this point is the telescope mount. Personally I would prefer a 48" F/3 from a stable substrate over the sandwich any day. I have a friend who is building a 48" F/4, and it's not a huge engineering job, by the way. However, I will not doom your project to failure - I encourage you to persevere. I will simply offer some thoughts and advice. I think your biggest issue is the aluminum backing changing dimension with fluctuating temperature. I have seen what aluminum bonded to glass can do, and it can be a big problem. That might account for the serious astigmatism you are seeing. If you can keep it at a constant temperature while you work and test, you might see improved results. OK, point made. On a lighter note.... Anish wrote: > I was wondering if anyone's ever used emoticon text to describe telescopes > I came up with a few (assuming target FOV at right) > Newtonian reflector : ( \ I like it, but the obstruction on that Newtonian appears to be >=100%, so I'd suggest this: / ( / \ There might be a bit of a central depression in that mirror, but at least some light is getting to the focal plane. It's bigger than the refractors, too. :o Mike Lockwood Lockwood Custom Optics _______________________________________________ ATM mailing list http://www.atmlist.net/ From vla at copper.net Thu Mar 19 05:50:47 2009 From: vla at copper.net (vladimir sacek) Date: Wed, 18 Mar 2009 16:50:47 -0400 Subject: [ATM] C1 glass References: <49C11E2E.9030607@rcn.com> Message-ID: <009901c9a80b$38576cd0$e34ef804@Handsome> All-spherical systems for this meniscus seem just fine. This one is with smaller secondary, 280mm f/3.75/13.6: R1: -434.19mm thickness: 29.34 medium: H-BSC2 R2: -450.77 to primary: 860 Rp: -2100 to secondary: -788 Rs: -770 and this one with larger secondary, f/3.64/10.7: R1: -434.19mm thickness: 29.34 medium: H-BSC2 R2: -450.77 to primary: 800 Rp: -2030 to secondary: -710 Rs: -960 Neither system is fully optimized, but correction levels are quite good. The first one is 0.015 wave RMS on axis, and 0.062 wave RMS 0.5 degree off-axis (best image surface). The second one is 0.013 wave RMS on axis, and 0.034 wave RMS 0.5 degree off. Residual coma and astigmatism are practically inconsequential, without even paying any attention to them. Best field curvature in both is nearly identical to the secondary mirror r.o.c. Any other system variation is possible, with smaller secondary in general requiring longer primary. The corrector seems not to be quite optimally corrected for spherochromatism (the 0.97 factor not applied), so that all wavelengths nearly focus at paraxial focus, instead at ~0.9 zone. But it is still low: with 0.116 wave RMS error at 430nm, it is still well within apochromatic correction. Vla From jkoptic at juno.com Thu Mar 19 06:19:44 2009 From: jkoptic at juno.com (Jarvis Krumbein) Date: Wed, 18 Mar 2009 14:19:44 -0700 Subject: [ATM] Impossible? - larger refractor Message-ID: <20090318.141944.140.0.jkoptic@juno.com> I thought the central zones on each lens could use a little re-figureing. \ / /\ \ / / \ ) ( ( ) / \ \ / / \ \/ Jarvis Krumbein On Wed, 18 Mar 2009 12:19:48 -0400 "astroguy at nas.com" writes: > > Ok, here is a larger refractor, take "that" reflector guys!!!! > > \ / /\ > \ / / \ > l l l l > / \ \ / > / \ \/ > > > Kreig > > > _________________________________________________________________ > > "There might be a bit of a central depression in that mirror, but at > > least some light is getting to the focal plane. It's bigger than > the > refractors, too. :o " > > > Original Message: > ----------------- > From: Mike Lockwood melockwo at uiuc.edu > Date: Wed, 18 Mar 2009 10:47:02 -0600 > To: atm at atmlist.net > Subject: [ATM] Impossible? I think not. > > > Hi, > > Ted Cohen wrote: > > A 48-inch F3 with any glass thickness is impossible for an > amateur. > > By hand, it would probably take about 10 years to complete just > the > > mirror. Furthermore, the glass and the tool would both be too > heavy > > to lift. The glass would be difficult to mount, and would require > a > > huge engineering job to design the appropriate telescope tube and > > mounting. After 10 years of work, you might find that the figure > on > > the glass is so bad, that it is only equivalent to the power of a > > 6-inch mirror. The cost, complexity and difficulty of the project > > increases exponentially with the size of the mirror. Also, an F/3 > > > parabola is very difficult to figure accurately without expensive > > equipment. You're better off sticking to what everyone else is > doing > > in the 8"-inch F/6 to F/10 range, which can be achieved relatively > > > quickly and accurately. > > Interesting - at first I thought that had to be sarcasm to be so > negative, but then I realized it was to be taken literally. It is > one > thing to politely inform a fellow list member of the difficulties of > a > project, but it is quite another to all but guarantee failure. Dave > has > been pushing the envelope for a while now and sharing his successes > and > failures with the list. I think you owe him an apology. > > I found that post ironic (I could have said hypocritical) after I > read > that you were working on this: > > Ted Cohen wrote: > > 23" x 3/4" floating in 3/8" layer of pitch with 1" thick > > aluminum plate backing. The focal ratio has crept down to about > 3.9 > > (I was originally targeting 4.75) The tool is dental stone > > approximately 4"-5" thick about 11" diameter (40%-50% of mirror > > diameter). Worked TOT 55-gallon barrel with concrete platform. My > > target correction is 1/3-1/4 wave peak to valley with no turned > edge. > > I anticipate another six months of figuring at the rate I'm going. > My > > biggest worry at this point is the telescope mount. > > Personally I would prefer a 48" F/3 from a stable substrate over the > > sandwich any day. I have a friend who is building a 48" F/4, and > it's > not a huge engineering job, by the way. > > However, I will not doom your project to failure - I encourage you > to > persevere. I will simply offer some thoughts and advice. > > I think your biggest issue is the aluminum backing changing > dimension > with fluctuating temperature. I have seen what aluminum bonded to > glass > can do, and it can be a big problem. That might account for the > serious > astigmatism you are seeing. If you can keep it at a constant > temperature while you work and test, you might see improved results. > > OK, point made. On a lighter note.... > > Anish wrote: > > I was wondering if anyone's ever used emoticon text to describe > telescopes > > I came up with a few (assuming target FOV at right) > > Newtonian reflector : ( \ > > I like it, but the obstruction on that Newtonian appears to be > >=100%, > so I'd suggest this: > > / > ( / > \ > > There might be a bit of a central depression in that mirror, but at > least some light is getting to the focal plane. It's bigger than > the > refractors, too. :o > > Mike Lockwood > Lockwood Custom Optics > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > > > > -------------------------------------------------------------------- > mail2web.com ? What can On Demand Business Solutions do for you? > http://link.mail2web.com/Business/SharePoint > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > ____________________________________________________________ Digital Photography - Click Now. http://thirdpartyoffers.juno.com/TGL2141/fc/BLSrjpTDvmTjokK9gQpzEq0Tn3Zi8GcaJe3lLdOsOcnHCDAn2fUjTkG0My0/ From geoniko at otenet.gr Thu Mar 19 06:23:22 2009 From: geoniko at otenet.gr (George Nikolidakis) Date: Wed, 18 Mar 2009 23:23:22 +0200 Subject: [ATM] Williams optics FLT 98 Special Edition Message-ID: <001101c9a80f$c4305f10$4c911d30$@gr> Hi fellows Yesterday I received the new FLT 98 Special Edition Special Edition means that the lenses are matched by the William Yang and come with measuring interferometer by AstroOptik. It is supposed to be a Very Limited Edition and optically excellent . If you see the advertisement in astromart you will find phrases like "extra high quality" And "This optics surpass even the 110 mm TEC delivered FLT by a great margin" http://www.astromart.com/classifieds/details.asp?classified_id=611889 I Have to say that the overall construction is excellent with an impressive focuser 3.5 inch. I uploaded some photos here : http://geonik.homeip.net/home/Equipment/ApochromaticRefractor/tabid/140/Defa ult.aspx Where I need your help is in the included interferometer report. http://geonik.homeip.net/home/tmp/tabid/135/Default.aspx Well about it I have to comment the follows and I like to hear your opinions. The peak to valley result is 1/4.1 waves measured in 632.8 nm That means about 1/3.55 waves peak to valley measured in 550 nm as commonly used. That is a medium to bad lens as the absolute boundary to evaluate a lens as acceptable (Rayleigh Limit) is 1/4 waves and better , that means this lens is nothing special at least for sure do not worth the word optical excellent and extra high quality regards the Peak to valley measure. Of course I know this not the only criterion to evaluate an optical lens. So the RMS value is measured to 1/23.8 in 632nm means about 1/21 Waves in 550nm, this an acceptable value but again is nothing special and far way to optically excellent. finally , the Strehl ratio 0.933 is simple a good value If we consider the optical quality standards (resource http://www.rfroyce.com/standards.htm) And according to the reference table and the included interferometer report 1.The P-V 1/3.55 = 0.279 (550 nm) is below the Rayleigh Limit 2.The RMS value ~ 0.04824 (550nm ) is about below the Good 3.The Strehl Ratio 0.933 is about Good. My conclusion is that this scope is far beyond the optically excellent and extra high quality. Please let me know your opinions and where am I wrong in the above? George Nikolidakis From rmay at nethere.com Thu Mar 19 06:40:29 2009 From: rmay at nethere.com (Bob May) Date: Wed, 18 Mar 2009 13:40:29 -0800 Subject: [ATM] help with an old meade dob mirror cell References: <49C01AF4.8040305@suttonsonline.us> <49C01DBF.1070007@simoivanov.com> Message-ID: <000e01c9a812$3f660ca0$8f78fea9@amd> The best thing is to rebuild the mirror cell so that it is lighter and has a lot more space for air to flow and put a fan behind the mirror. There are some things that you can do to reduce the problem tho. First is to keep the telescope cool, leaving it in the house rather than in the garage or car on warm times and out in the garage when it is cooler than the house. This will minimize the amount of cooling needed to equalize to the night air. Next is to remove the mirror and cell if possible and let it cool first to the night air while you are letting your eyes adjust to the night sky. Also putting the telescope vertical while letting it cool down helps. A fan pulling the air from the front of the telescope also helps and the little 12V fans with a small 12V battery (use a lead acid type battery and you can charge it from the car's lighter plug) to run the fan. One of the problems which you really can't do anything about is that the mirror is a full thickness mirror of plate glass and that means that it's not going to cool and respond as well as a Pyrex (low temp coefficient glass) mirror would. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Thu Mar 19 06:58:19 2009 From: rmay at nethere.com (Bob May) Date: Wed, 18 Mar 2009 13:58:19 -0800 Subject: [ATM] C1 glass References: Message-ID: <003501c9a814$a9981b20$8f78fea9@amd> BSC2 is in the database but there are other letters attached as a prefix as another noted. One thing that I will note as Dominic (I think) noted is that different glasses didn't change the spot diagrams very much at all. Another thing to note is that the spotted corrector is remarked as being an approximate design so I'd expect that its spot diagrams won't be all that good. Also remember that the Mak design is just a variation of the Cassegrain design with a corrector "parabolizing" the primary wavefront. You will get the spots that you'd be getting with a parabolic primary and spherical secondary with a spotted Mak - basically junk compared to what it should be. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Thu Mar 19 07:03:25 2009 From: rmay at nethere.com (Bob May) Date: Wed, 18 Mar 2009 14:03:25 -0800 Subject: [ATM] BSC2 glass References: Message-ID: <004001c9a815$5d9698e0$8f78fea9@amd> I thought I'd get a piece of glass tested (an old flint with a number that I couldn't find at the time) and called up Newport. They wanted a piece of the glass with a flat surface on it and they'd run it through their refractometer. I gave up on that when I finally found a listing for the glass that seemed right. I willnote that without papers stating exactly the melt's index, any optical glass just won't make a "perfect" scope. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From s.c.koehler at gmail.com Thu Mar 19 07:02:33 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Wed, 18 Mar 2009 17:02:33 -0500 Subject: [ATM] Williams optics FLT 98 Special Edition In-Reply-To: <001101c9a80f$c4305f10$4c911d30$@gr> References: <001101c9a80f$c4305f10$4c911d30$@gr> Message-ID: <8d3a545d0903181502r1622bae5lc48437de4521a1f4@mail.gmail.com> George, I fooled around with analyzing the synthetic interferogram from your report. I get the same wavefront map as on the report (approximately), and I get a Strehl ratio of .930. I think it's odd that they left in the coma. Usually, you remove that, because it is usually due to interferometer misalignment. Even if the coma was in the glass, you could remove it by careful collimation. (You can see a little coma in the PSF image in the report.) If you remove the coma, the Strehl ratio goes up from 0930 to .959. -- Steve Koehler From rmay at nethere.com Thu Mar 19 07:08:36 2009 From: rmay at nethere.com (Bob May) Date: Wed, 18 Mar 2009 14:08:36 -0800 Subject: [ATM] judging impossible from plausible, was Re: Impossible? I think not. References: <25466.159.121.96.200.1236894058.squirrel@webmail.peak.org><49C12586.1010301@uiuc.edu> <20090318121715.khnqkxvhk4880c4s@bbastrodesigns.com> Message-ID: <004901c9a816$168dabe0$8f78fea9@amd> One thing that I'll note in all of this is that going up to a large mirror by steps will be a bit faster than jumping in and trying to do the large mirror all at once. You're working on a 12" right now and finding some interesting problems. Those and other problems will pop up in the larger mirrors adn the solving of the problems with the smaller mirrors will allow them to be taken care of with the next mirror. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From geoniko at otenet.gr Thu Mar 19 07:46:29 2009 From: geoniko at otenet.gr (George Nikolidakis) Date: Thu, 19 Mar 2009 00:46:29 +0200 Subject: [ATM] Williams optics FLT 98 Special Edition In-Reply-To: <8d3a545d0903181502r1622bae5lc48437de4521a1f4@mail.gmail.com> References: <001101c9a80f$c4305f10$4c911d30$@gr> <8d3a545d0903181502r1622bae5lc48437de4521a1f4@mail.gmail.com> Message-ID: <000001c9a81b$608397f0$218ac7d0$@gr> Thanks Steve I am not so familiar with these measures I know only the basics and Just for the mirrors. I have constructed a 20" truss tube telescope in the past and I enjoyed very match. I am very new to the APO World. Seems that I need some more lessons. Can you say a few words more about the quality of this APO examining the report. Thanks George. -----Original Message----- From: Stephen Koehler [mailto:s.c.koehler at gmail.com] Sent: Thursday, March 19, 2009 12:03 AM To: George Nikolidakis Cc: atm at atmlist.net Subject: Re: [ATM] Williams optics FLT 98 Special Edition George, I fooled around with analyzing the synthetic interferogram from your report. I get the same wavefront map as on the report (approximately), and I get a Strehl ratio of .930. I think it's odd that they left in the coma. Usually, you remove that, because it is usually due to interferometer misalignment. Even if the coma was in the glass, you could remove it by careful collimation. (You can see a little coma in the PSF image in the report.) If you remove the coma, the Strehl ratio goes up from 0930 to .959. -- Steve Koehler From wkitty42 at windstream.net Thu Mar 19 11:19:12 2009 From: wkitty42 at windstream.net (waldo kitty) Date: Wed, 18 Mar 2009 21:19:12 -0500 Subject: [ATM] Williams optics FLT 98 Special Edition In-Reply-To: <001101c9a80f$c4305f10$4c911d30$@gr> References: <001101c9a80f$c4305f10$4c911d30$@gr> Message-ID: <49C1ABA0.3030704@windstream.net> George Nikolidakis wrote: > Hi fellows > Yesterday I received the new FLT 98 Special Edition > Special Edition means that the lenses are matched by the William Yang > and come with measuring interferometer by AstroOptik. > It is supposed to be a Very Limited Edition and optically excellent . my current and only question is about the above statement... are you saying that you ordered one of these lens', have received and tested it and that's where your numbers come from or are those numbers their's? -- NOTE: NEW EMAIL ADDRESS!! _\/ (@@) Waldo Kitty, Waldo's Place USA __ooO_( )_Ooo_____________________ telnet://bbs.wpusa.dynip.com _|_____|_____|_____|_____|_____|_____ http://www.wpusa.dynip.com ____|_____|_____|_____|_____|_____|____ ftp://ftp.wpusa.dynip.com _|_Eat_SPAM_to_email_me!_YUM!__|_____ wkitty42 -at- windstream.net From wa4guu at verizon.net Thu Mar 19 12:02:25 2009 From: wa4guu at verizon.net (Jerry) Date: Wed, 18 Mar 2009 23:02:25 -0400 Subject: [ATM] Williams optics FLT 98 Special Edition In-Reply-To: <001101c9a80f$c4305f10$4c911d30$@gr> Message-ID: <79CF1B8EADEA4ABEBABCDBB178BA293C@D85SJB21> You are using an orange caliper to measure an apple. Refractors are a bit more complicated than reflectors. In reflectors all colors of light take the same path to focus. It is not so with refractors and the commonly accepted measures of a reflector quality do not suit refractors so well. You cannot really just factor the difference of wavelength of the red interferometric test to green light. The lens probably has its best spherical correction in green. Measuring the red does not tell you the green correction or the blue correction, or for that matter any other color but the red. Roland Christen of ASTRO-PHYSICS fame used to have some information on this subject on the web... somewhere. I suggest you search using his name as one of the keywords. Jerry -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of George Nikolidakis Sent: Wednesday, March 18, 2009 5:23 PM To: atm at atmlist.net Subject: [ATM] Williams optics FLT 98 Special Edition Hi fellows Yesterday I received the new FLT 98 Special Edition Special Edition means that the lenses are matched by the William Yang and come with measuring interferometer by AstroOptik. It is supposed to be a Very Limited Edition and optically excellent . If you see the advertisement in astromart you will find phrases like "extra high quality" And "This optics surpass even the 110 mm TEC delivered FLT by a great margin" http://www.astromart.com/classifieds/details.asp?classified_id=611889 I Have to say that the overall construction is excellent with an impressive focuser 3.5 inch. I uploaded some photos here : http://geonik.homeip.net/home/Equipment/ApochromaticRefractor/tabid/140/Defa ult.aspx Where I need your help is in the included interferometer report. http://geonik.homeip.net/home/tmp/tabid/135/Default.aspx Well about it I have to comment the follows and I like to hear your opinions. The peak to valley result is 1/4.1 waves measured in 632.8 nm That means about 1/3.55 waves peak to valley measured in 550 nm as commonly used. That is a medium to bad lens as the absolute boundary to evaluate a lens as acceptable (Rayleigh Limit) is 1/4 waves and better , that means this lens is nothing special at least for sure do not worth the word optical excellent and extra high quality regards the Peak to valley measure. Of course I know this not the only criterion to evaluate an optical lens. So the RMS value is measured to 1/23.8 in 632nm means about 1/21 Waves in 550nm, this an acceptable value but again is nothing special and far way to optically excellent. finally , the Strehl ratio 0.933 is simple a good value If we consider the optical quality standards (resource http://www.rfroyce.com/standards.htm) And according to the reference table and the included interferometer report 1.The P-V 1/3.55 = 0.279 (550 nm) is below the Rayleigh Limit 2.The RMS value ~ 0.04824 (550nm ) is about below the Good 3.The Strehl Ratio 0.933 is about Good. My conclusion is that this scope is far beyond the optically excellent and extra high quality. Please let me know your opinions and where am I wrong in the above? George Nikolidakis _______________________________________________ ATM mailing list http://www.atmlist.net/ From wa4guu at verizon.net Thu Mar 19 12:13:16 2009 From: wa4guu at verizon.net (Jerry) Date: Wed, 18 Mar 2009 23:13:16 -0400 Subject: [ATM] Williams optics FLT 98 Special Edition In-Reply-To: <79CF1B8EADEA4ABEBABCDBB178BA293C@D85SJB21> Message-ID: This has some very useful info to get you started. http://geogdata.csun.edu/~voltaire/roland/index.html One of these days... I'm gonna get one of them "Big As tro Physics scopes. Jerry -----Original Message----- From: Jerry Roland Christen of ASTRO-PHYSICS fame used to have some information on this subject on the web... somewhere. I suggest you search using his name as one of the keywords. Jerry -----Original Message----- From: atm-bounces at atmlist.net [mailto:atm-bounces at atmlist.net] On Behalf Of George Nikolidakis Sent: Wednesday, March 18, 2009 5:23 PM To: atm at atmlist.net Subject: [ATM] Williams optics FLT 98 Special Edition Hi fellows Yesterday I received the new FLT 98 Special Edition From wa4guu at verizon.net Thu Mar 19 12:28:49 2009 From: wa4guu at verizon.net (Jerry) Date: Wed, 18 Mar 2009 23:28:49 -0400 Subject: [ATM] [SPAM] RE: Williams optics FLT 98 Special Edition In-Reply-To: Message-ID: <91EE1DF023FF475EAD84256E0147E18F@D85SJB21> Specifically http://geogdata.csun.edu/~voltaire/roland/APO_testing.html -----Original Message----- From: Jerry This has some very useful info to get you started. http://geogdata.csun.edu/~voltaire/roland/index.html -----Original Message----- From: Jerry Roland Christen of ASTRO-PHYSICS fame used to have some information on this subject on the web... somewhere. I suggest you search using his name as one of the keywords. Jerry -----Original Message----- From: George Nikolidakis Hi fellows Yesterday I received the new FLT 98 Special Edition From wa4guu at verizon.net Thu Mar 19 12:31:50 2009 From: wa4guu at verizon.net (Jerry) Date: Wed, 18 Mar 2009 23:31:50 -0400 Subject: [ATM] Williams optics FLT 98 Special Edition Message-ID: <8C8B0F8C074A478DADF4C6A65B631143@D85SJB21> Specifically http://geogdata.csun.edu/~voltaire/roland/APO_testing.html -----Original Message----- From: Jerry This has some very useful info to get you started. http://geogdata.csun.edu/~voltaire/roland/index.html -----Original Message----- From: Jerry Roland Christen of ASTRO-PHYSICS fame used to have some information on this subject on the web... somewhere. I suggest you search using his name as one of the keywords. Jerry -----Original Message----- From: George Nikolidakis Hi fellows Yesterday I received the new FLT 98 Special Edition From dlwebb at canit.se Thu Mar 19 17:57:37 2009 From: dlwebb at canit.se (Dominic-Luc Webb) Date: Thu, 19 Mar 2009 09:57:37 +0100 (MET) Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 Message-ID: I am afraid I must now post without further delay a warning about the 11.25" Mak Club design. I have gone through the Nov/Dec 1957 S&T articles by Norman A Burts and also Maksutov Circular #15 (1957). Both contain schematics and prescription. I am afraid I will have to now warn, as I long suspected, that there is sufficient ambiguity between the different sources that no assumptions can be made as to whether Hayward C1 or BSC2 was used for the meniscus. Roger at S&T explicitly stated to this list in 23 Mar 1998 the Mak Club ordered C1 corrector blanks. Most of the writing on the glass type choice in S&T regarded testing of the secondary, not the meniscus corrector. Key to this test is that the refractive index of sodium light for the glass chosen must be numerically equal to the eccentricity of the Cass secondary. Circular #15 schematic states in the schematic only that BSC2 glass be used (ND/VD 517645). However, the Cass secondary eccentricity is then clearly stated as 1.523 both in this circular and in the Dec 1957 S&T article. The value 1.523 cannot possibly be BSC2, but is a perfect match for C1. Similarly, the effective focal length of the system in both articles cannot possibly be obtained using a secondary with an eccentrity equal to the refractive index of BSC2, but can be obtained with C1. Hence, there is good reason to believe the Cass secondary was C1 glass. The S%T article appears somewhat ambiguous later in the text when it is stated that BSC2 glass can be used instead of C1. I think what was meant was that BSC2 could instead be used for the secondary, not for the meniscus corrector. It seems entirely possible the Mak Club ordered C1 glass for the corrector and C1 or BSC2 for secondary. Given this uncertainty, the advice I have been given to test my particular meniscus glass, seems the wisest way forward. My glass is from the original purchase of the Mak Club, but the BSC2 vs C1 glass type was never adequately proven. The mission now is to precisely determine if this glass is of C1 vs BSC2 lineage and its exact characteristics by direct optical tests on the actual specimen I have. Dominic From vladimir.galogaza1 at zg.t-com.hr Thu Mar 19 20:01:27 2009 From: vladimir.galogaza1 at zg.t-com.hr (Vladimir Galogaza) Date: Thu, 19 Mar 2009 12:01:27 +0100 Subject: [ATM] Williams optics FLT 98 Special Edition References: <001101c9a80f$c4305f10$4c911d30$@gr> <8d3a545d0903181502r1622bae5lc48437de4521a1f4@mail.gmail.com> Message-ID: Stephen, I noticed that interferogram on a test sheet was marked as "synthetic". I miss the purpose of including synthetic interferogram into a test sheet for an optics. I would expect a real interferogram which served for reported analysis results. If synthetic interferograms was made from analysis results than no wander that when analyzed again it produced them back. It is a kind of test of integrity of analysis program not the optics. What do you think? Regards Vladimir. From geoniko at otenet.gr Thu Mar 19 23:32:50 2009 From: geoniko at otenet.gr (George Nikolidakis) Date: Thu, 19 Mar 2009 16:32:50 +0200 Subject: [ATM] Williams optics FLT 98 Special Edition In-Reply-To: <49C1ABA0.3030704@windstream.net> References: <001101c9a80f$c4305f10$4c911d30$@gr> <49C1ABA0.3030704@windstream.net> Message-ID: <000601c9a89f$94f413a0$bedc3ae0$@gr> Hi the interferometer report came with telescope. Was Their report... George -----Original Message----- From: waldo kitty [mailto:wkitty42 at windstream.net] Sent: Thursday, March 19, 2009 4:19 AM To: George Nikolidakis Cc: atm at atmlist.net Subject: Re: [ATM] Williams optics FLT 98 Special Edition George Nikolidakis wrote: > Hi fellows > Yesterday I received the new FLT 98 Special Edition > Special Edition means that the lenses are matched by the William Yang > and come with measuring interferometer by AstroOptik. > It is supposed to be a Very Limited Edition and optically excellent . my current and only question is about the above statement... are you saying that you ordered one of these lens', have received and tested it and that's where your numbers come from or are those numbers their's? -- NOTE: NEW EMAIL ADDRESS!! _\/ (@@) Waldo Kitty, Waldo's Place USA __ooO_( )_Ooo_____________________ telnet://bbs.wpusa.dynip.com _|_____|_____|_____|_____|_____|_____ http://www.wpusa.dynip.com ____|_____|_____|_____|_____|_____|____ ftp://ftp.wpusa.dynip.com _|_Eat_SPAM_to_email_me!_YUM!__|_____ wkitty42 -at- windstream.net From s.c.koehler at gmail.com Thu Mar 19 23:39:23 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Thu, 19 Mar 2009 09:39:23 -0500 Subject: [ATM] [interferometry] Re: Williams optics FLT 98 Special Edition In-Reply-To: References: <001101c9a80f$c4305f10$4c911d30$@gr> <8d3a545d0903181502r1622bae5lc48437de4521a1f4@mail.gmail.com> Message-ID: <8d3a545d0903190739i69c17b7ai9b9902f87cff3521@mail.gmail.com> Vladimir, > I noticed that interferogram on a test sheet was marked as > "synthetic". > I miss the purpose of including synthetic interferogram > into a test sheet for an optics. > I would expect a real interferogram which served for > ?reported analysis results. > If synthetic interferograms was made from analysis > results than no wander that when analyzed again it produced > them back. It is a kind of test of integrity of analysis program > not the optics. > What do you think? The synthetic interferogram allowed me to load the wavefront into my program. The same thing could have been done from a set of Zernike coefficients. In fact, you might think of the synthetic interferogram as the graphical equivalent of Zernike coefficients--one can be turned into the other relatively easily. A real interferogram has some advantages, but also some disadvantages. If only one interferogram is shown, there is probably not enough data to reconstruct the wavefront, since the reported wavefront was probably derived from an average of multiple interferograms. Also, a real interferogram can have quality issues that make a size-reduced image in a test report difficult to analyze. Apropos to this, one of the articles Jerry pointed to on Roland Christen's site talks about what a synthetic interferogram is good for: In fact, Quick Fringe software allows for the averaging of the various interference fringe runs, and then synthesizes a clean pattern that can be displayed in the final report. Some may call this a "fake" interferogram, but it is based on real data and is more representative of the actual performance than any one fringe pattern. -- Steve Koehler From s.c.koehler at gmail.com Thu Mar 19 23:53:53 2009 From: s.c.koehler at gmail.com (Stephen Koehler) Date: Thu, 19 Mar 2009 09:53:53 -0500 Subject: [ATM] Williams optics FLT 98 Special Edition In-Reply-To: <000001c9a81b$608397f0$218ac7d0$@gr> References: <001101c9a80f$c4305f10$4c911d30$@gr> <8d3a545d0903181502r1622bae5lc48437de4521a1f4@mail.gmail.com> <000001c9a81b$608397f0$218ac7d0$@gr> Message-ID: <8d3a545d0903190753i450c38b3j4133f30f09d2f8c3@mail.gmail.com> George, > Can you say a few words more about the quality of this APO examining the report. I'm not really qualified to comment on this. As Jerry pointed out, the interferometry was done in red (632nm wavelength), so you would expect some spherical aberration. The main contribution I wanted to make was to point out that that the interferometry report left in coma, and perhaps it should have been removed. I don't know very much about the manufacture of refractors, but I suspect the decision to rate this optic top quality was done using some sort of qualitative null test. Interferometry was probably done to document the result, not to make the decision. (I could be wrong here.) Given that the interferometry report does not appear to have all the information you need to assess the quality, I think you need to trust the manufacturer. I would suggest doing a careful star test, and if everything looks good, be satisfied. -- Steve Koehler From vorblesnak at peak.org Fri Mar 20 03:55:54 2009 From: vorblesnak at peak.org (vorblesnak at peak.org) Date: Thu, 19 Mar 2009 11:55:54 -0700 (PDT) Subject: [ATM] Impossible 48's and ??? Message-ID: <43044.159.121.96.200.1237488954.squirrel@webmail.peak.org> Well, I am glad I was able to shock and awe. Ted, no apology needed, thank you for submitting one. Lets get back to the science folks. Much of the technology for the mirror is quite common. I used much of it over the last few years making thin junk that got thrown away. BUT having stretched the patience of the list more than once most of that went unreported. It was no loss to you, trust me on this. The initial concept for the mirror had been to fuse the glass to the foam with heat. Other than the basic fusion issues there is no foam available in the 48 inch range. I continue to work with the engineer at Pittsburgh Corning looking for a solution to this one, but for now I must set it aside. The next possible solution is adhesive. There is a long history of failure with that approach. I argued with some folks last night about it. I am working on a 12 inch, as Bob May pointed out. This is a materials test, not a mirror. Many people expressed concern over the foam's ability to handle the stress of mirror work and I wondered about the adhesive I chose. Well, I worked it with all the techniques I could think of. It now has over 40 hours on the machine in different orientations. The only damage I was able to do to the foam backer was when I put the mirror on top. The fingers on the Hindle machine damaged the foam due to the stress of the push / pull action of the overarm. This puck of foam was glued together from a earlier disaster. The glass was glued on. I believe adhesive will work in the short run. But how will time affect the figure of the mirror? Well, this test puck had no figure. At least I didn't think it did until I looked. It has some figure but was never set up to polish out, just to be abused. It just goes to show you, physics is our friend. Rub a chunk of glass long enough and you will get a mirror. So now I am thinking maybe I will try and polish it out and then run some environmental tests on it. That is where I am going today. Do I need to use adhesive? Couldn't the glass just rest on the puck of glass foam? It is an excellent buffer material. See, there are questions to answer here. The technology should be available to the average amateur. And it can be. I post here to further the art. I am very much on the bleeding edge and many times it is the part that gets thrown away. You can be a part of it by doing what you are doing right now. Call it bullshit, tell me what I have missed. Share a strange idea on how it might work. Ask for a blank, I'll send you one. It could take a while as I am not a production facility. Many hands can figure this out, it is not out of our reach. We are using technology first tried in the 1600s that really has not changed that much since. I think the ends are worth the work. MORE GRINDING LESS THINKING!! David Davis Toledo, OR 97391 From jonas.zaveckas at gmail.com Fri Mar 20 18:13:39 2009 From: jonas.zaveckas at gmail.com (Jonas) Date: Fri, 20 Mar 2009 11:13:39 +0200 Subject: [ATM] Pits during fine grinding Message-ID: <49C35E43.3090206@gmail.com> I am trying to grind my first mirror. Used K180 as start for fine grinding (after doing rough grinding with K80). After 2 hours switched to K320. I'm using tile and dental stone tool for this. The surface structure changes nicely as fine grinding proceeds. The problem is that I'm constantly getting tiny holes (not scratches) on the glass surface. They look much larger to me than current grit size and can be 'nicely' seen while holding the mirror before lamp light. The strange thing is that I was getting them while grinding with K180 also. Can this be caused by some small tile edges falling off? Average density is about 1 per 2 square cm. Would say, more to the edges. Or maybe I use too much pressure and some pieces of glass just fall off because of that? Mirror is 6" so it is too light to make grinding action by its own weight? Or I just worry too much as a first timer? Jonas From alaskawolfjoe at hotmail.com Sat Mar 21 00:07:46 2009 From: alaskawolfjoe at hotmail.com (lance clarke) Date: Fri, 20 Mar 2009 11:07:46 -0400 Subject: [ATM] Pits during fine grinding In-Reply-To: <49C35E43.3090206@gmail.com> References: <49C35E43.3090206@gmail.com> Message-ID: There will always be some pits that are larger than the others. You just need to figure out if you've ground out all of the pits from the previous grade. Take a magic marker, and mark a few of the big ones on the other side of the glass, and after a few wets, see if they are still there. Also, check to see that the surface is the same on the outer part of the glass as the center. If you are working mirror on top, it will tend to finish earlier than the edge, so compare them. Grit isn't uniform size, so there will always be different size pits. In making my first mirror, I chased those pits around for far too long. Lance > Date: Fri, 20 Mar 2009 11:13:39 +0200 > From: jonas.zaveckas at gmail.com > To: atm at atmlist.net > Subject: [ATM] Pits during fine grinding > > I am trying to grind my first mirror. Used K180 as start for fine > grinding (after doing rough grinding with K80). After 2 hours switched > to K320. I'm using tile and dental stone tool for this. > > The surface structure changes nicely as fine grinding proceeds. The > problem is that I'm constantly getting tiny holes (not scratches) on the > glass surface. They look much larger to me than current grit size and > can be 'nicely' seen while holding the mirror before lamp light. The > strange thing is that I was getting them while grinding with K180 also. > Can this be caused by some small tile edges falling off? Average density > is about 1 per 2 square cm. Would say, more to the edges. > > Or maybe I use too much pressure and some pieces of glass just fall off > because of that? Mirror is 6" so it is too light to make grinding action > by its own weight? > > Or I just worry too much as a first timer? > > Jonas > _______________________________________________ > ATM mailing list http://www.atmlist.net/ _________________________________________________________________ Chat with the whole group, and bring everyone together. http://go.microsoft.com/?linkid=9650735 From rmay at nethere.com Sat Mar 21 05:41:34 2009 From: rmay at nethere.com (Bob May) Date: Fri, 20 Mar 2009 12:41:34 -0800 Subject: [ATM] Pits during fine grinding References: <49C35E43.3090206@gmail.com> Message-ID: <003401c9a99c$43103de0$8f78fea9@amd> I'll note taht the glass cracks in different directoins depending upon randomness. You may have a whole bunch of nice fine divots in the mirror aind one big wide one. The wide one may be actually a lot shallower than the little typical ones. doesn't mean that they're bad, it's just that the glass broke in a shallow direction. IN addition, the depth to which a chip off of the mirror goes is a variable so you will have some deepter pits. This is the reason why you have to go down through the grits - gradually make all of the pits smaller and take out the larger grit's pits that were made in the glass. Find the largest looking pits in the glass and look to see if they are still there after another wet of the grit and if they go away then you are done with that grit, even if other big pits seem to happen. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From jonas.zaveckas at gmail.com Sat Mar 21 18:51:15 2009 From: jonas.zaveckas at gmail.com (Jonas) Date: Sat, 21 Mar 2009 11:51:15 +0200 Subject: [ATM] Pits during fine grinding In-Reply-To: References: <49C35E43.3090206@gmail.com> Message-ID: <49C4B893.6020906@gmail.com> lance clarke wrote: > There will always be some pits that are larger than the others. You just need to figure out if you've ground out all of the pits from the previous grade. Take a magic marker, and mark a few of the big ones on the other side of the glass, and after a few wets, see if they are still there. Also, check to see that the surface is the same on the outer part of the glass as the center. If you are working mirror on top, it will tend to finish earlier than the edge, so compare them. > > I think I did it. Marked a few of largest pits and made them almost to disappear making them smaller than the new ones that seems to be created at a constant rate. It seems to be caused (as Bob May wrote in his message) by some glass chipping specifics. Surface seems to be identical all over the mirror so that should be the criteria to move on. I've already did good one hour with 320 before and additional 1.5 hours now so I think I'll go to Microgrit WCA 25 my (the next grit that I have) without wasting 320 and grinding time any more... It's a pity that we don't have any grinding classes or some experts here locally, because it's always better to see once than hear many times. All procedures are described pretty well in many sources but such subtle details always. Most often its written that you should move to next grit after all pits from previous grit will be gone. It seems that it is almost impossible to achieve because event smaller grit can sometimes produce large pits? Thank you for your messages. Jonas From russjocoy at hotmail.com Sun Mar 22 04:10:56 2009 From: russjocoy at hotmail.com (Russell Jocoy) Date: Sat, 21 Mar 2009 15:10:56 -0400 Subject: [ATM] Crossroads, go back or keep going? Message-ID: To all on the list, Hello, Well to start with I must tell you some background. I have been working on a 17.5" pyrex mirror f-4.5 which is 1-5/8" thick. When a bought the mirror about 6 years ago it was part of a warehouse of glass and machines. It just so happens this disk was still mounted to a grinding machine and is the last 17.5 ever ground by Coulter. Well, the disk had very even surface depth, consistant all over after testing with my spherometer. The surface looked to me to be about 10 micron. I have been polishing for about 15 hours, here and there on my machine. It looks great on the test stand, and is quite reflective now, I have a big problem.. Laser and led's still show a 'frost" on close inspection. I fear that it was only ground to 25 micron....oops! I have 15 hrs of polish on this jewel and I fear I may have to go back to 15mic and start all over.. Is it possible to polish out?? I listed photos on the ATM Drall site but I don't know how to get the links to this page..can someone help, with both problems? Russ Jocoy _________________________________________________________________ Get quick access to your favorite MSN content with Internet Explorer 8. http://ie8.msn.com/microsoft/internet-explorer-8/en-us/ie8.aspx?ocid=B037MSN55C0701A From rmay at nethere.com Sun Mar 22 04:42:47 2009 From: rmay at nethere.com (Bob May) Date: Sat, 21 Mar 2009 11:42:47 -0800 Subject: [ATM] Pits during fine grinding References: <49C35E43.3090206@gmail.com> <49C4B893.6020906@gmail.com> Message-ID: <000401c9aa5d$375d1f60$8f78fea9@amd> There's a fairly good spread of us about the US and even a bit over in the old countries. Sometimes a call out willl find somebody not too far away. I'm in the San Diego area and am conducting (along with another guy) a freeform groupt of mirrormaking and other things. We've had guys drive more than a hundred miles just to see what is going on and sometimes even start mirrors which they have finished at home. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From rmay at nethere.com Sun Mar 22 04:45:16 2009 From: rmay at nethere.com (Bob May) Date: Sat, 21 Mar 2009 11:45:16 -0800 Subject: [ATM] Crossroads, go back or keep going? References: Message-ID: <000701c9aa5d$8fda5220$8f78fea9@amd> Time to go back and so some grinding. A long session with 5 mircon should do it but you may want to do 12 first. Yes, it was last ground to 25 which means that it may not be finished even there. Bob May rmay at nethere.com http: slash /nav.to slash bobmay http: slash /bobmay dot astronomy.net From jbentz at inreach.com Sun Mar 22 05:01:14 2009 From: jbentz at inreach.com (Jan Bentz) Date: Sat, 21 Mar 2009 13:01:14 -0700 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 In-Reply-To: References: Message-ID: <49C5478A.8010505@inreach.com> Dominic -- You are certainly doing the right thing by getting a test on the glass but I'll toss another turd in the punchbowl by saying that I have always thought that C-1 was Haywards rough equivilant to Cornings Pyrex. I have a 22" x 3" generated blank that was used decades ago in the 22" f/10 Schmidt -Cass from Celestron and was told by Tom Johnson that it was C-1 from Hayward . I also have a partially finished 11" corrector shell from Jacque Lebreque who bought it during the original purchase by the Mak club. He assured me it was BSC-2 Haywards clone of BK-7. It differs from BK-7 by only 1 or 2 digits in the 4th decimal place. I had also been told that refractors had been successfully made with it using designs using BK-7. Here is a design I've worked up for a 11" f/21 planetary scope using BK-7 numbers: R1 = -18.3415 t1 = 1.0 R2 = -18.9182 t2 = 39.6 R3 = -94.518 t3 = -37.957 R4 = -25.309 This prescription will place the focus about 11.5" behind the primary and give a spot size of about .0004" (C-F) or 1/3 Airy size and be diffraction ltd in the visible out to the edge of a 2" dia flat field. There is some chromatic differance of magnification but is well controlled with careful radii on the shell. With a 5.3 amplification for the secondary it can be kept to about 22% of the CA. On paper there is no aspherization needed. Jan Bentz Dominic-Luc Webb wrote: >I am afraid I must now post without further delay a warning >about the 11.25" Mak Club design. > >I have gone through the Nov/Dec 1957 S&T articles by >Norman A Burts and also Maksutov Circular #15 (1957). >Both contain schematics and prescription. I am afraid >I will have to now warn, as I long suspected, that there >is sufficient ambiguity between the different sources >that no assumptions can be made as to whether Hayward >C1 or BSC2 was used for the meniscus. > >Roger at S&T explicitly stated to this list in 23 Mar 1998 >the Mak Club ordered C1 corrector blanks. Most of the writing >on the glass type choice in S&T regarded testing of the secondary, >not the meniscus corrector. Key to this test is that the >refractive index of sodium light for the glass chosen must >be numerically equal to the eccentricity of the Cass secondary. >Circular #15 schematic states in the schematic only that BSC2 >glass be used (ND/VD 517645). However, the Cass secondary >eccentricity is then clearly stated as 1.523 both in this >circular and in the Dec 1957 S&T article. The value 1.523 cannot >possibly be BSC2, but is a perfect match for C1. Similarly, >the effective focal length of the system in both articles >cannot possibly be obtained using a secondary with an >eccentrity equal to the refractive index of BSC2, but can >be obtained with C1. Hence, there is good reason to believe >the Cass secondary was C1 glass. The S%T article appears >somewhat ambiguous later in the text when it is stated >that BSC2 glass can be used instead of C1. I think what was >meant was that BSC2 could instead be used for the secondary, >not for the meniscus corrector. > >It seems entirely possible the Mak Club ordered C1 glass >for the corrector and C1 or BSC2 for secondary. > >Given this uncertainty, the advice I have been given to >test my particular meniscus glass, seems the wisest way >forward. My glass is from the original purchase of the >Mak Club, but the BSC2 vs C1 glass type was never >adequately proven. > >The mission now is to precisely determine if this glass >is of C1 vs BSC2 lineage and its exact characteristics >by direct optical tests on the actual specimen I have. > >Dominic > >_______________________________________________ >ATM mailing list http://www.atmlist.net/ > > > From mbartels at bbastrodesigns.com Sun Mar 22 05:42:03 2009 From: mbartels at bbastrodesigns.com (Mel Bartels) Date: Sat, 21 Mar 2009 13:42:03 -0700 Subject: [ATM] Crossroads, go back or keep going? In-Reply-To: References: Message-ID: <006201c9aa65$82705af0$875110d0$@com> >>> Hello, Well to start with I must tell you some background. I have been working on a 17.5" pyrex mirror f-4.5 which is 1-5/8" thick. When a bought the mirror about 6 years ago it was ... I have 15 hrs of polish on this jewel and I fear I may have to go back to 15mic and start all over.. Is it possible to polish out?? I listed photos on the ATM Drall site but I don't know how to get the links to this page..can someone help, with both problems? <<< 15 hours??? Are you applying any pressure at all??? A 17.5 inch should be polished in several hours given sufficient pressure. In the old days mirrors would be polished from 600 silicon carbide. So you can certainly continue polishing. I'm guessing 2x to 3x more time will be needed. But do add pressure! Mel Bartels From simo at simoivanov.com Sun Mar 22 06:27:44 2009 From: simo at simoivanov.com (simo ivanov) Date: Sun, 22 Mar 2009 06:27:44 +0900 Subject: [ATM] Crossroads, go back or keep going? In-Reply-To: References: Message-ID: <49C55BD0.1070100@simoivanov.com> Russ: Here's the link to your pictures. http://www.atmlist.net/contrib/russjocoy-at-hotmail-dot-com/Russ%20Jocoy%2017.5%22%20f4.5/ I've moved the files to the folder you created, and renamed them (added a .jpg extension) so that they open automatically by most browsers. Best, Russell Jocoy wrote: > > > To all on the list, > > > > Hello, Well to start with I must tell you some background. I have been working on a 17.5" pyrex mirror f-4.5 which is 1-5/8" thick. When a bought the mirror about 6 years ago it was part of a warehouse of glass and machines. It just so happens this disk was still mounted to a grinding machine and is the last 17.5 ever ground by Coulter. > > Well, the disk had very even surface depth, consistant all over after testing with my spherometer. The surface looked to me to be about 10 micron. I have been polishing for about 15 hours, here and there on my machine. It looks great on the test stand, and is quite reflective now, I have a big problem.. Laser and led's still show a 'frost" on close inspection. I fear that it was only ground to 25 micron....oops! > > I have 15 hrs of polish on this jewel and I fear I may have to go back to 15mic and start all over.. Is it possible to polish out?? I listed photos on the ATM Drall site but I don't know how to get the links to this page..can someone help, with both problems? > > Russ Jocoy > > _________________________________________________________________ > Get quick access to your favorite MSN content with Internet Explorer 8. > http://ie8.msn.com/microsoft/internet-explorer-8/en-us/ie8.aspx?ocid=B037MSN55C0701A > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From richard at foucault.co.uk Sun Mar 22 07:25:32 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Sat, 21 Mar 2009 22:25:32 +0000 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 In-Reply-To: <49C5478A.8010505@inreach.com> References: <49C5478A.8010505@inreach.com> Message-ID: <937984197.20090321222532@foucault.co.uk> Hello Jan, Saturday, March 21, 2009, 8:01:14 PM, you wrote: > Here is a design I've worked up for a 11" f/21 planetary scope using > BK-7 numbers: Not sure what I'm doing different Jan, but with your figures and Schott N-BK7 I'm seeing spot size around twice the Airy disk on axis, and 4 times at 50mm field diameter, using F,d,C wavelengths. Focus is at 1255.236305 from spherical secondary on a flat image plane. -- Best regards, Richard in the UK From vla at copper.net Sun Mar 22 08:02:47 2009 From: vla at copper.net (vladimir sacek) Date: Sat, 21 Mar 2009 19:02:47 -0400 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 References: <49C5478A.8010505@inreach.com> <937984197.20090321222532@foucault.co.uk> Message-ID: <000801c9aa79$27e39200$e84cf804@Handsome> It looks like Jan described in OSLO. Vla ----- Original Message ----- From: "Richard in the UK" To: "Jan Bentz" Sent: Saturday, March 21, 2009 6:25 PM Subject: Re: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 > Hello Jan, > > Saturday, March 21, 2009, 8:01:14 PM, you wrote: > >> Here is a design I've worked up for a 11" f/21 planetary scope using >> BK-7 numbers: > > Not sure what I'm doing different Jan, but with your figures and > Schott N-BK7 I'm seeing spot size around twice the Airy disk on axis, > and 4 times at 50mm field diameter, using F,d,C wavelengths. Focus is > at 1255.236305 from spherical secondary on a flat image plane. > From richard at foucault.co.uk Sun Mar 22 08:25:13 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Sat, 21 Mar 2009 23:25:13 +0000 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 In-Reply-To: <000801c9aa79$27e39200$e84cf804@Handsome> References: <49C5478A.8010505@inreach.com> <937984197.20090321222532@foucault.co.uk> <000801c9aa79$27e39200$e84cf804@Handsome> Message-ID: <1996915373.20090321232513@foucault.co.uk> Hello vladimir, Saturday, March 21, 2009, 11:02:47 PM, you wrote: > It looks like Jan described in OSLO. I'm not sure how you would know that from the info given, but if true, how is it relevant?. Physics is Physics. -- Best regards, Richard in the UK From vla at copper.net Sun Mar 22 09:00:41 2009 From: vla at copper.net (vladimir sacek) Date: Sat, 21 Mar 2009 20:00:41 -0400 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 References: <49C5478A.8010505@inreach.com><937984197.20090321222532@foucault.co.uk><000801c9aa79$27e39200$e84cf804@Handsome> <1996915373.20090321232513@foucault.co.uk> Message-ID: <000a01c9aa81$3ed99600$6a4df804@Handsome> Richard, > >> It looks like Jan described in OSLO. > > I'm not sure how you would know that from the info given, but if true, > how is it relevant?. Physics is Physics. > I've simply put Jan's system data into OSLO, and it resulted in near perfectly corrected Maksutov-Cassegrain, as he said it does. The relevance of it is obvious, since it responds to your post stating that the data hasn't produced such system. In OSLO, all the wavelengths from 400nm to 700nm are comfortably within the Airy disc on axis, and nearly so at the edge of 2-inch field diameter (best image surface). Vla From russjocoy at hotmail.com Sun Mar 22 10:31:46 2009 From: russjocoy at hotmail.com (Russell Jocoy) Date: Sat, 21 Mar 2009 21:31:46 -0400 Subject: [ATM] FW: Crossroads, go back or keep going? In-Reply-To: <49C55BD0.1070100@simoivanov.com> References: <49C55BD0.1070100@simoivanov.com> Message-ID: > Date: Sun, 22 Mar 2009 06:27:44 +0900 > From: simo at simoivanov.com > To: russjocoy at hotmail.com > CC: atm at atmlist.net > Subject: Re: [ATM] Crossroads, go back or keep going? > > Russ: > > Here's the link to your pictures. > > http://www.atmlist.net/contrib/russjocoy-at-hotmail-dot-com/Russ%20Jocoy%2017.5%22%20f4.5/ > > I've moved the files to the folder you created, and renamed them (added > a .jpg extension) so that they open automatically by most browsers. > > Best, > > > > > Russell Jocoy wrote: > > > > > > To all on the list, > > > > > > > > Hello, Well to start with I must tell you some background. I have been working on a 17.5" pyrex mirror f-4.5 which is 1-5/8" thick. When a bought the mirror about 6 years ago it was part of a warehouse of glass and machines. It just so happens this disk was still mounted to a grinding machine and is the last 17.5 ever ground by Coulter. > > > > Well, the disk had very even surface depth, consistant all over after testing with my spherometer. The surface looked to me to be about 10 micron. I have been polishing for about 15 hours, here and there on my machine. It looks great on the test stand, and is quite reflective now, I have a big problem.. Laser and led's still show a 'frost" on close inspection. I fear that it was only ground to 25 micron....oops! > > > > I have 15 hrs of polish on this jewel and I fear I may have to go back to 15mic and start all over.. Is it possible to polish out?? I listed photos on the ATM Drall site but I don't know how to get the links to this page..can someone help, with both problems? > > > > Russ Jocoy > > > > _________________________________________________________________ > > Get quick access to your favorite MSN content with Internet Explorer 8. > > http://ie8.msn.com/microsoft/internet-explorer-8/en-us/ie8.aspx?ocid=B037MSN55C0701A > > _______________________________________________ > > ATM mailing list http://www.atmlist.net/ > _________________________________________________________________ Hotmail? is up to 70% faster. Now good news travels really fast. http://windowslive.com/online/hotmail?ocid=TXT_TAGLM_WL_HM_70faster_032009 From gfbrandenburg at yahoo.com Sun Mar 22 12:05:55 2009 From: gfbrandenburg at yahoo.com (Guy Brandenburg) Date: Sat, 21 Mar 2009 20:05:55 -0700 (PDT) Subject: [ATM] Crossroads, go back or keep going? Message-ID: <19253.69319.qm@web111514.mail.gq1.yahoo.com> We had someone using polishing pads almost completely polish out an 8 inch mirror in 2 hours. Only a few small specks visible under a 60x microscope. He was pushing hard, however, and using very little polishing compound. Guy Brandenburg, Washington, DC My home page on astronomy, mathematics, education: http://home.earthlink.net/~gfbranden/GFB_Home_Page.html or else http://tinyurl.com/r6fh2 ============================= "Education isn't rocket science. It's much, much harder." (Author unknown) --- On Sat, 3/21/09, Mel Bartels wrote: > From: Mel Bartels > Subject: Re: [ATM] Crossroads, go back or keep going? > To: "'ATM list'" > Date: Saturday, March 21, 2009, 4:42 PM > >>> > ? ? Hello, Well to start with I must tell you > some background. I have been > working on a 17.5" pyrex mirror f-4.5 which is 1-5/8" > thick. When a bought > the mirror about 6 years ago it was ... > ? ? I have 15 hrs of polish on this jewel and I > fear I may have to go back > to 15mic and start all over.. Is it possible to polish > out?? I listed photos > on the ATM Drall site but I don't know how to get the links > to this > page..can someone help, with both problems? > <<< > > > 15 hours??? Are you applying any pressure at all???? A > 17.5 inch should be > polished in several hours given sufficient pressure.? > In the old days > mirrors would be polished from 600 silicon carbide.? > So you can certainly > continue polishing.? I'm guessing 2x to 3x more time > will be needed.? But do > add pressure! > > Mel Bartels > > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From rflrs at rcn.com Sun Mar 22 12:16:30 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Sat, 21 Mar 2009 22:16:30 -0500 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 In-Reply-To: <937984197.20090321222532@foucault.co.uk> References: <49C5478A.8010505@inreach.com> <937984197.20090321222532@foucault.co.uk> Message-ID: <49C5AD8E.90901@rcn.com> Richard in the UK wrote: > Hello Jan, > > Saturday, March 21, 2009, 8:01:14 PM, you wrote: > >> Here is a design I've worked up for a 11" f/21 planetary scope using >> BK-7 numbers: > > Not sure what I'm doing different Jan, but with your figures and > Schott N-BK7 I'm seeing spot size around twice the Airy disk on axis, > and 4 times at 50mm field diameter, using F,d,C wavelengths. Focus is > at 1255.236305 from spherical secondary on a flat image plane. > Refocus it so that the hook at the aperture is crossing, not the paraxial focus -- subtract about 1 mm from that focus distance. From donald_clement at yahoo.com Sun Mar 22 12:23:43 2009 From: donald_clement at yahoo.com (don clement) Date: Sat, 21 Mar 2009 20:23:43 -0700 (PDT) Subject: [ATM] Crossroads, go back or keep going? Message-ID: <100330.84379.qm@web34206.mail.mud.yahoo.com> Guy, Polishing pads -Ahh the ol? Robert Johnson ?Crossroads Blues? deal with the devil. I prefer the Cream version with Bruce, Baker, and Clapton . Or is it Mayall with the I was looking back to see If she was looking back to see If I was looking back at her -Don --- On Sat, 3/21/09, Guy Brandenburg wrote: > From: Guy Brandenburg > Subject: Re: [ATM] Crossroads, go back or keep going? > To: "'ATM list'" , "Mel Bartels" > Date: Saturday, March 21, 2009, 8:05 PM > > We had someone using polishing pads almost completely > polish out an 8 inch mirror in 2 hours. Only a few small > specks visible under a 60x microscope. He was pushing hard, > however, and using very little polishing compound. > > Guy Brandenburg, Washington, DC > My home page on astronomy, mathematics, education: > http://home.earthlink.net/~gfbranden/GFB_Home_Page.html > or else > http://tinyurl.com/r6fh2 > > ============================= > "Education isn't rocket science. It's much, much harder." > (Author unknown) > > > > --- On Sat, 3/21/09, Mel Bartels > wrote: > > > From: Mel Bartels > > Subject: Re: [ATM] Crossroads, go back or keep going? > > To: "'ATM list'" > > Date: Saturday, March 21, 2009, 4:42 PM > > >>> > > ? ? Hello, Well to start with I must tell you > > some background. I have been > > working on a 17.5" pyrex mirror f-4.5 which is 1-5/8" > > thick. When a bought > > the mirror about 6 years ago it was ... > > ? ? I have 15 hrs of polish on this jewel and I > > fear I may have to go back > > to 15mic and start all over.. Is it possible to > polish > > out?? I listed photos > > on the ATM Drall site but I don't know how to get the > links > > to this > > page..can someone help, with both problems? > > <<< > > > > > > 15 hours??? Are you applying any pressure at all???? > A > > 17.5 inch should be > > polished in several hours given sufficient > pressure.? > > In the old days > > mirrors would be polished from 600 silicon carbide.? > > So you can certainly > > continue polishing.? I'm guessing 2x to 3x more time > > will be needed.? But do > > add pressure! > > > > Mel Bartels > > > > > > > > > > _______________________________________________ > > ATM mailing list http://www.atmlist.net/ > > > > > ? ? ? > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From mbartels at bbastrodesigns.com Sun Mar 22 12:37:07 2009 From: mbartels at bbastrodesigns.com (Mel Bartels) Date: Sat, 21 Mar 2009 20:37:07 -0700 Subject: [ATM] Crossroads, go back or keep going? In-Reply-To: <100330.84379.qm@web34206.mail.mud.yahoo.com> References: <100330.84379.qm@web34206.mail.mud.yahoo.com> Message-ID: <000001c9aa9f$7d752140$785f63c0$@com> >>> Polishing pads -Ahh the ol? Robert Johnson ?Crossroads Blues? deal with the devil. I prefer the Cream version with Bruce, Baker, and Clapton . Or is it Mayall with the I was looking back to see If she was looking back to see If I was looking back at her <<< I've never used pads myself, though a few have in my classes. I use microfacetting, a good solid fine grinding, heavy pressure, Gugolz pitch on the soft-medium side and adequate wetting with relatively heavy cerium oxide. Polish times (all pits gone): 8 inch - 2 hrs 12 inch - 4 hrs 24 inch - 6 hrs Mel Bartels From gfbrandenburg at yahoo.com Sun Mar 22 12:48:04 2009 From: gfbrandenburg at yahoo.com (Guy Brandenburg) Date: Sat, 21 Mar 2009 20:48:04 -0700 (PDT) Subject: [ATM] Crossroads, go back or keep going? Message-ID: <447603.45370.qm@web111515.mail.gq1.yahoo.com> We only use the pads at the beginning, to get it polished out. We often use 3 micron microgrit right before the pads. Then switch to pitch for the figuring. Final figuring with rouge. Guy --- On Sat, 3/21/09, don clement wrote: > From: don clement > Subject: Re: [ATM] Crossroads, go back or keep going? > To: "'ATM list'" > Date: Saturday, March 21, 2009, 11:23 PM > > > Guy, > > Polishing pads -Ahh the ol? Robert Johnson ?Crossroads > Blues? deal with the devil. I prefer the Cream version > with Bruce, Baker, and Clapton .? Or is it? Mayall > with the I was looking back to see If she was looking back > to see If I was looking back at her > > -Don > > > --- On Sat, 3/21/09, Guy Brandenburg > wrote: > > > From: Guy Brandenburg > > Subject: Re: [ATM] Crossroads, go back or keep going? > > To: "'ATM list'" , > "Mel Bartels" > > Date: Saturday, March 21, 2009, 8:05 PM > > > > We had someone using polishing pads almost completely > > polish out an 8 inch mirror in 2 hours. Only a few > small > > specks visible under a 60x microscope. He was pushing > hard, > > however, and using very little polishing compound. > > > > Guy Brandenburg, Washington, DC > > My home page on astronomy, mathematics, education: > > http://home.earthlink.net/~gfbranden/GFB_Home_Page.html > > or else > > http://tinyurl.com/r6fh2 > > > > ============================= > > "Education isn't rocket science. It's much, much > harder." > > (Author unknown) > > > > > > > > --- On Sat, 3/21/09, Mel Bartels > > wrote: > > > > > From: Mel Bartels > > > Subject: Re: [ATM] Crossroads, go back or keep > going? > > > To: "'ATM list'" > > > Date: Saturday, March 21, 2009, 4:42 PM > > > >>> > > > ? ? Hello, Well to start with I must tell you > > > some background. I have been > > > working on a 17.5" pyrex mirror f-4.5 which is > 1-5/8" > > > thick. When a bought > > > the mirror about 6 years ago it was ... > > > ? ? I have 15 hrs of polish on this jewel and > I > > > fear I may have to go back > > > to 15mic and start all over.. Is it possible to > > polish > > > out?? I listed photos > > > on the ATM Drall site but I don't know how to get > the > > links > > > to this > > > page..can someone help, with both problems? > > > <<< > > > > > > > > > 15 hours??? Are you applying any pressure at > all???? > > A > > > 17.5 inch should be > > > polished in several hours given sufficient > > pressure.? > > > In the old days > > > mirrors would be polished from 600 silicon > carbide.? > > > So you can certainly > > > continue polishing.? I'm guessing 2x to 3x more > time > > > will be needed.? But do > > > add pressure! > > > > > > Mel Bartels > > > > > > > > > > > > > > > _______________________________________________ > > > ATM mailing list http://www.atmlist.net/ > > > > > > > > > ? ? ? > > _______________________________________________ > > ATM mailing list http://www.atmlist.net/ > > > > > ? ? ? > _______________________________________________ > ATM mailing list http://www.atmlist.net/ From hermit at outofoptions.org Sun Mar 22 13:15:23 2009 From: hermit at outofoptions.org (hermit) Date: Sun, 22 Mar 2009 00:15:23 -0400 Subject: [ATM] Impossible 48's and ??? In-Reply-To: <43044.159.121.96.200.1237488954.squirrel@webmail.peak.org> References: <43044.159.121.96.200.1237488954.squirrel@webmail.peak.org> Message-ID: <49C5BB5B.3020708@outofoptions.org> I asked before, but I may have missed it. You have used these in the field? No problems with differential cooling of the plate and foam? Ken Lowther vorblesnak at peak.org wrote: > Well, I am glad I was able to shock and awe. Ted, no apology needed, thank > you for submitting one. > > Lets get back to the science folks. > > Much of the technology for the mirror is quite common. I used much of it > over the last few years making thin junk that got thrown away. BUT having > stretched the patience of the list more than once most of that went > unreported. It was no loss to you, trust me on this. > > The initial concept for the mirror had been to fuse the glass to the foam > with heat. Other than the basic fusion issues there is no foam available > in the 48 inch range. I continue to work with the engineer at Pittsburgh > Corning looking for a solution to this one, but for now I must set it > aside. > > The next possible solution is adhesive. There is a long history of failure > with that approach. I argued with some folks last night about it. I am > working on a 12 inch, as Bob May pointed out. This is a materials test, > not a mirror. Many people expressed concern over the foam's ability to > handle the stress of mirror work and I wondered about the adhesive I > chose. Well, I worked it with all the techniques I could think of. It now > has over 40 hours on the machine in different orientations. The only > damage I was able to do to the foam backer was when I put the mirror on > top. The fingers on the Hindle machine damaged the foam due to the stress > of the push / pull action of the overarm. This puck of foam was glued > together from a earlier disaster. The glass was glued on. I believe > adhesive will work in the short run. But how will time affect the figure > of the mirror? Well, this test puck had no figure. At least I didn't think > it did until I looked. It has some figure but was never set up to polish > out, just to be abused. It just goes to show you, physics is our friend. > Rub a chunk of glass long enough and you will get a mirror. > > So now I am thinking maybe I will try and polish it out and then run some > environmental tests on it. That is where I am going today. Do I need to > use adhesive? Couldn't the glass just rest on the puck of glass foam? It > is an excellent buffer material. > > See, there are questions to answer here. The technology should be > available to the average amateur. And it can be. I post here to further > the art. I am very much on the bleeding edge and many times it is the part > that gets thrown away. You can be a part of it by doing what you are doing > right now. Call it bullshit, tell me what I have missed. Share a strange > idea on how it might work. Ask for a blank, I'll send you one. It could > take a while as I am not a production facility. Many hands can figure this > out, it is not out of our reach. We are using technology first tried in > the 1600s that really has not changed that much since. I think the ends > are worth the work. > > MORE GRINDING LESS THINKING!! > > David Davis > Toledo, OR 97391 > > > > _______________________________________________ > ATM mailing list http://www.atmlist.net/ > From richard at foucault.co.uk Sun Mar 22 20:18:10 2009 From: richard at foucault.co.uk (Richard in the UK) Date: Sun, 22 Mar 2009 11:18:10 +0000 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 In-Reply-To: <000a01c9aa81$3ed99600$6a4df804@Handsome> References: <49C5478A.8010505@inreach.com><937984197.20090321222532@foucault.co.uk><000801c9aa79$27e39200$e84cf804@Handsome> <1996915373.20090321232513@foucault.co.uk> <000a01c9aa81$3ed99600$6a4df804@Handsome> Message-ID: <948949146.20090322111810@foucault.co.uk> Hello vladimir, Sunday, March 22, 2009, 12:00:41 AM, you wrote: > I've simply put Jan's system data into OSLO, and it resulted in near > perfectly corrected Maksutov-Cassegrain, Doesn't that worry you though, that two professional optics programs produce different results from the same data?. It is impossible to say which one is right and which one is wrong, as optimising the data in Zemax will produce the same sort of results as you indicated, but that data put into OSLO then produces poor results. > In OSLO, all the wavelengths from 400nm to 700nm > are comfortably within the Airy disc on axis, and nearly so at the edge of > 2-inch field diameter (best image surface). Didn't Jan say that the spot size was one third of the Airy disk on axis? (I can't access his original msg atm). Also, you say "best image surface". What do you mean by that?. I assume you a surface of the correct final radius which is what we would all normally use, *but* Jan specifically said a flat surface which is why I used a flat surface in my comparison. This difference between Oslo and Zemax has happened several times before and I would like to get to the bottom of it. Are they looking at the same info differently or does one of them have a fundamental problem?. It's probably just me forgetting something fundamental but I would like to know. Eg, it is easy for one person to be using best image surface and the other to be using a flat plane, hence me being pedantic over it. -- Best regards, Richard in the UK From vla at copper.net Sun Mar 22 23:22:53 2009 From: vla at copper.net (vladimir sacek) Date: Sun, 22 Mar 2009 10:22:53 -0400 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 References: <49C5478A.8010505@inreach.com><937984197.20090321222532@foucault.co.uk><000801c9aa79$27e39200$e84cf804@Handsome><1996915373.20090321232513@foucault.co.uk><000a01c9aa81$3ed99600$6a4df804@Handsome> <948949146.20090322111810@foucault.co.uk> Message-ID: <002a01c9aaf9$b1279630$0d5ff804@Handsome> Hello Richard, > > Doesn't that worry you though, that two professional optics programs > produce different results from the same data. While that is possible, I didn't have a reason to rule out some type of user error. In fact, I am still inclined to think that is the case (not that raytracinmg softwares, even the best ones, are perfect, but we certainly aren't). Another possibility is that software computer files became corrupted. >> In OSLO, all the wavelengths from 400nm to 700nm >> are comfortably within the Airy disc on axis, and nearly so at the edge >> of >> 2-inch field diameter (best image surface). > > Didn't Jan say that the spot size was one third of the Airy disk on > axis? (I can't access his original msg atm). Also, you say "best image > surface". What do you mean by that?. I assume you a surface of the > correct final radius which is what we would all normally use, *but* > Jan specifically said a flat surface which is why I used a flat > surface in my comparison. > Yes, that is what he stated and, as long as we stay in the F-C range, it is what my version of OSLO shows. Best image surface is a term fairly commonly used for a surface connecting best point-image foci in the image space of a telescope (or camera). In presence of astigmatism, it is usually called "median" (astigmatic) surface. Jan did state that the system is diffraction limited "out to the edge of a 2" dia flat field". But that doesn't necessarily imply that the system does have flat field; I never assumed it does, because I happened to know that Cassegrain- like systems in such configuration can't have it. > This difference between Oslo and Zemax has happened several times > before and I would like to get to the bottom of it. Are they looking > at the same info differently or does one of them have a fundamental > problem. My feeling is that OSLO does have some - probably small - glitches (haven't used ZEMAX, so can't tell). I don't know how specifically either of them works, so can only guess if one of them is right, and the other wrong, or they are both wrong. We can always pull out the theory, and see what it is supposed to be (not really a simple task with systems producing significant higher-order aberrations, though). The focus distance that you have - 1255.236mm - does differ from what I've got with the original data (1253.151mm, although I may have slightly rounded off some values when converting to mm), but it doesn't have to imply an error by itself. When I make a minor change to corrector's radii, to -465.9 and -480.6mm, the focus distance becomes 1257.218, but the correction is actually better (0.0141 wave RMS e-light vs. 0.0216 original, and nearly proportional further reduction in blur size). Vla From vla at copper.net Sun Mar 22 23:30:19 2009 From: vla at copper.net (vladimir sacek) Date: Sun, 22 Mar 2009 10:30:19 -0400 Subject: [ATM] C1 glass References: <002b01c9a7de$7203cdc0$a159f804@Handsome> <001201c9a7e2$4f459ee0$725af804@Handsome> Message-ID: <003901c9aafa$bb413ad0$0d5ff804@Handsome> I wrote: > Here's all it takes to determine MCT >> system parameters very close to its optimized version: >> >> R1~R(1-2t-0.01F){[T(n+2)(n-1)^2]/2(n^3)(1-s)R}^0.25 >> R2=R1-{[1-(1/n^2)]T/0.97} >> >> where R1 and R2 are the front and rear corrector radius, respectively, >> R is the primary mirror r.o.c., "n" is the glass refractive, T the >> corrector >> center thickness, and s=[(m-1)(m+1)^2]/m^3, "m" being the secondary >> magnification. Note that R, R1 and R2 are all numerically negative. >> > Dropped t=T/R Also F=the primary mirror F#, and s=k[(m-1)(m+1)^2]/m^3, with "k" being the relative height of marginal ray at the secondary in units of semi-aperture (equals minimum relative secondary size). I think I've got it all right now. Vla From rflrs at rcn.com Sun Mar 22 23:53:11 2009 From: rflrs at rcn.com (Richard F.L.R. Snashall) Date: Sun, 22 Mar 2009 09:53:11 -0500 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 In-Reply-To: References: Message-ID: <49C650D7.1060503@rcn.com> Dominic-Luc Webb wrote: > I am afraid I must now post without further delay a warning > about the 11.25" Mak Club design. Suppose you have an optimized Maksutov Newtonian: *LENS DATA mak01-24 SRF RADIUS THICKNESS APERTURE RADIUS GLASS SPE NOTE OBJ -- 1.0000e+20 3.3161e+17 AIR AST -- 23.07589 139.70000 A AIR 2 -434.40545 28.00000 145.00000 H_BSC2 C 3 -450.55402 1581.13180 145.00000 AIR 4 -2386.95892 -1217.61123 152.40475 REFLECT 5 -- -- 3.85298 AIR 6 -- -- 3.85298 AIR IMS -1215.23892 -- 3.85223 You can insert a size-limited convex secondary to make a Cassegrain: *LENS DATA mak01-24c SRF RADIUS THICKNESS APERTURE RADIUS GLASS SPE NOTE OBJ -- 1.0000e+20 6.9813e+16 AIR AST -- 23.07589 139.70000 A AIR 2 -434.40545 28.00000 145.00000 H_BSC2 C 3 -450.55402 1581.13180 145.00000 AIR 4 -2386.95892 -922.58179 148.27544 REFLECT 5 -787.62551 922.58179 36.57524 REFLECT * 6 -2386.95892 P 254.00000 10.40055 AIR IMS -271.74593 -- 3.20410 *CONIC AND POLYNOMIAL ASPHERIC DATA SRF CC AD AE AF AG 5 -2.2773e+00 -- 6.3041e-14 -- -- but it reintroduces coma, making the visually diffraction limited field is only about +/-0.04 degrees. You can increase this some, say to about +/-0.05 by moving the corrector closer to the secondary. However, when I considered having a section of the tube actually reversible (note also the slight increase in CA): *LENS DATA mak01-24s SRF RADIUS THICKNESS APERTURE RADIUS GLASS SPE NOTE OBJ -- 1.0000e+20 1.7453e+17 AIR AST -- -23.25359 142.87500 A AIR 2 450.55402 28.00000 145.00000 H_BSC2 C 3 434.40545 1024.27917 145.00000 AIR 4 -2386.95892 -924.27917 144.29080 REFLECT 5 -785.82780 924.27917 36.57732 REFLECT * 6 -2386.95892 P 254.00000 14.55799 AIR IMS -223.15397 -- 8.51689 *CONIC AND POLYNOMIAL ASPHERIC DATA SRF CC AD AE AF AG 5 -4.3708e+00 -- 4.2843e-14 -- -- the visually diffraction limited field is roughly doubled. There is a cost here in that the Visual Strehl in the center field goes down to 0.9822 from 0.9978. Have I seen this somewhere, before? From jbentz at inreach.com Mon Mar 23 02:14:24 2009 From: jbentz at inreach.com (Jan Bentz) Date: Sun, 22 Mar 2009 10:14:24 -0700 Subject: [ATM] 11.25" Mak Club glass: Uncertainty in BSC2 vs C1 In-Reply-To: <002a01c9aaf9$b1279630$0d5ff804@Handsome> References: <49C5478A.8010505@inreach.com><937984197.20090321222532@foucault.co.uk><000801c9aa79$27e39200$e84cf804@Handsome><1996915373.20090321232513@foucault.co.uk><000a01c9aa81$3ed99600$6a4df804@Handsome> <948949146.20090322111810@foucault.co.uk> <002a01c9aaf9$b1279630$0d5ff804@Handsome> Message-ID: <49C671F0.1000104@inreach.com> Richard and Vlad -- The program I used was the old Beam 3 which I prefer for simple telescopic systems over Zemax or Oslo. These are full featured programs as you know, more suitable for complex, non-diffraction limited, wide field systems like camera lenses or eyepieces where you want quantitative measures of distortion, PSF, ray intercept curves, MTF, wavefront maps etc. I am just lazy I guess but I find Beam 3 much easier and faster to use to say nothing of learning it in the 1st place. Anyway I can't really comment on what differences between Oslo and Zemax might account for the discrepancies. As for the field curvature which is about -21", I disregarded it and figured the spot size on a flat field situated between the center and the edge of the focal surface. If the image is looked at on a curved surface the C-F spot size is only a little larger at the edge of 2" field than in the center. But there is no need for it to be any better at the edge than on a flat field as it wouldn't be used visually at high power anyway only photographically. In these slow systems the Airy disc size corresponds more or less to the resolution of film or large CCD's anyway. The system is fairly sensitive to tolerances and in practice would likely have to be aspherized anyway. Jan Bentz vladimir sacek wrote: > Hello Richard, > >> >> Doesn't that worry you though, that two professional optics programs >> produce different results from the same data. > > > While that is possible, I didn't have a reason to rule out some type of > user error. In fact, I am still inclined to think that is the case > (not that raytracinmg > softwares, even the best ones, are perfect, but we certainly aren't). > Another > possibility is that software computer files became corrupted. > >>> In OSLO, all the wavelengths from 400nm to 700nm >>> are comfortably within the Airy disc on axis, and nearly so at the >>> edge of >>> 2-inch field diameter (best image surface). >> >> >> Didn't Jan say that the spot size was one third of the Airy disk on >> axis? (I can't access his original msg atm). Also, you say "best image >> surface". What do you mean by that?. I assume you a surface of the >> correct final radius which is what we would all normally use, *but* >> Jan specifically said a flat surface which is why I used a flat >> surface in my comparison. >> > Yes, that is what he stated and, as long as we stay in the F-C range, > it is what my version of OSLO shows. > > Best image surface is a term fairly commonly used for a surface > connecting > best point-image foci in the image space of a telescope (or camera). In > presence of astigmatism, it is usually called "median" (astigmatic) > surface. > > Jan did state that the system is diffraction limited "out to the edge > of a 2" > dia flat field". But that doesn't necessarily imply that the system > does have flat > field; I never assumed it does, because I happened to know that > Cassegrain- > like systems in such configuration can't have