[ATM] What can I do with this mirror?
Paul A. Valleli
valleli at rcn.com
Wed Jan 11 07:17:43 JST 2012
John,
You could use it in a lab to pick up a distant heat
source and bring it to a near- focus.
Two would make a great whispering chamber but its
mate is probably boxed in a hangar somewhere in NM.
Laser pointers are cheap, set up an array of them
pointed at the mirror and show how the beams are
focused.
Probably the most useful, would be to copy Don
Dilworth's "Space Ray" design of Relay Telescope
with an open set of struts supported at the end of a
baffle tube. Place a webcam or MalinCam at the focal
point , pointed at the mirror. Mount this OTA on a
simple Dob. Be sure the IR blocking filter has been
removed from the camera. One could do photometry in
the R, I, and IR bands on red stars.
Paul
---- Original message ----
Date: Tue, 10 Jan 2012 01:32:41 -0800
From: John Sutter <jds-ml at sutters.com>
Subject: Re: [ATM] What can I do with this mirror?
To: "Paul A. Valleli" <valleli at rcn.com>
Cc: atm at atmlist.net
>After reading your write-up on Thomas, I'd feel
bad doing anything>that might damage the mirror.
It seems like an artifact. I'll keep it>as a
novelty and use it for science demos at the local
school.>>Do you have recommendations for good
demos for kids? Kids love burning,>but probably
not on school property around here. Maybe a laser
pointer>on a pivot at the focal point after
talking about the properties of the>shape.>>I'll
add a copy of your write-up to the mirror's
paperwork too.>>Thanks for the great
information,>>-- John>>On 1/9/2012 10:46 PM, Paul
A. Valleli wrote:>> John,>> This mirror is not the
one I was thinking of. I left AOCC four months>>
before it was completed and the Visidyne System
was very similar but>> made at Optical Systems &
Technology, Inc, of Billerica MA., which was a>>
spin-off of Diffraction Limited of Bedford, MA.>>
Bill Brady had also worked at Itek and was my
replacement. Bill married>> the boss's daughter!>>
The test setup was as I thought, as it is one of
the best ways to test>> very steep mirrors.>> We
had a 24-inch Collimator that was built for the
Voyager Project and>> it had a series of
illuminated pinholes. The outgoing light was
captured>> by the mirror under test and relayed to
the side of the optical bench>> with a Newtonian
diagonal. The image spot was simply scanned with
a>> knife edge and the transverse motion measured
from the first hint of a>> shadow to total
extinction of the Foucault Pattern. Quick and
Dirty, but>> inexpensive.>> The 0.13mm would have
been measured with a micrometer.>> Note that the
zonal irregularity is only guessed to be <500 A,
or about>> 1/10th wave over a small zone width -
probably 1/2 to 1 inch.>> The Knife Edge test can
detect errors of 1/60th wave, provided the>>
source is only a few times larger than the
diffraction limited blur and>> bright enough to be
observed.>> This is what makes it a subjective
test - with a wide slit - say 0.010>> to 0.020", a
rough, zony mirror can look smooth, but the rms is
large>> and the Strehl Criterion low.>> Paul>>>>
---- Original message ---->>>>>> *Date:* Mon, 09
Jan 2012 11:03:23 -0800>> *From:* John Sutter
<jds-ml at sutters.com>>> *Subject:* Re: [ATM] What
can I do with this mirror?>> *To:* "Paul A.
Valleli" <valleli at rcn.com>>> *Cc:*
atm at atmlist.net>> >That's quite the coincidence.
Not what I was hoping to hear,>> but>there are
always possibilities. Worst case, I guess it could
end>> up as>a part of a Burning Man project.>>I
put up the scanned>> paperwork I have on it at:>>>
http://www.sutters.com/ATM_Stuff/20120108_mirror_docs.pdf>>It's
good>> to know it's not beryllium as
well.>>Thanks,>>-- John>>On 1/8/2012>> 8:43 PM,
Paul A. Valleli wrote:>> BOY ! are you lucky,
John,>> I was>> the project manager and optical
test engineer for this 24-inch>>>> Cass. System
and you provided just enough info for me to
uniquely>>>> identify it.>> It was made of 6061-T6
Aluminium Alloy and thermally>> stabilized for
very>> high altitude use, with liquid nitrogen
and>> oven baking cycles.>> The customer was
Visidyne Corp. a private>> contractor to the USAF
at>> Hanscom AFB in Bedford MA. They>>
sub-contracted the optics to Sylvania. I>> can't
tell you what it>> was used fo! r but it was
basically a light bucket>> to feed>> infrared
light to an IR spectrometer.>> >> In 1976,
opticians did not know how to polish bare aluminum
- it>> is>> technically far different from
pitch-polishing glass. The>> process>> procedure
was to machine the aluminum forging close to>>
shape, anneal the>> material, and then progressive
machine to final>> dimensions. after the>> first
set of thermal cycles, we apply a very>> thin
layer of electroless>> Nickel - a substance which
does not have>> a crystalline structure - it is>>
amorphous, just like glass, but>> the polishing is
done with pitch and>> sub-micron sized aluminum>>
oxide ( basically Sapphire).>> After collimation
testing to the>> parabolic figure, the mirror
was>> electroplated with pure Gold for>> 99%
reflectance from the red to thermal>> infrared
wavelengths.>> Plated Gold is much more durable
than vacuum>> coated Gold.>> I>> believe the spec.
was for a blur circle less than 0.13 mm or 130>>
microns.>> I am afraid for your sake, that that!
is about ten times>> the blur spot of>> a visual
scope and is very far from diffraction>> limited -
hence the>> 'light-bucket' designation. Modern
IR>> detectors have around 30 micron>> pixels, but
it is likely in those>> days, that they used a
single pixel of>> MerCadTel, cooled to>>
minus327F.>> I left AOCC in the Fall of 1976 and
they moved the>> operations to>> Sarasota, FL in
about 1980.That was a year after we>> made six
similar>> telescopes for the Mariner>>
Jupiter/Saturn/Uranus/Neptune "Grand Tour",>> now
known as the JPL>> Voyager Program. The primaries
were 20-inch>> diameter Nickel Plated>> Beryllium
primaries at F/0.8 ! - and>> hyperboloidal
secondaries.>>>> The rest is history, two of the
spacefraft are at the edge of the>> Solar>>
System, travelling a BILLION miles every three
years.>> What>> to do with the mirror ? You could
strip the Gold if you are>>>> comfortable about
working with Potassium Cyanide ! but the>>
underlying>> Nickel only has a reflectivity of
55%.>> How about a>> cigarette lighter?>> Starman
Paul>>>> ---- Original message>> ---->>>>>>
*Date:* Sun, 08 Jan 2012 01:53:41 -0800>> *From:*
John>> Sutter <jds-ml at sutters.com>>> *Subject:*
[ATM] What can I do with>> this mirror?>> *To:*
atm at atmlist.net>> >I picked up a 24" mirror at>>
auction a few years ago.>It was made>> in 1976. I
have a>> little>documentation on it, but few of
the figures>> mean>much to>> me.>>Details:>
Diameter: 24.4"> Clear Aperture: 24">>>
Centering>> Accuracy: w/in 0.050 (no units,
assuming ")> Final Focal>> Length:>> 35.5"> Vertex
Radius of Curvature: 71"> Shape of figured>>
surface:>> Parabaloid> Surface accuracy: <= 500 A>
Diameter of circle>> of>> least confusion: 80-100%
w/in 0.13 (no units, >assuming ")>>>>> Surface
finish: 80/50>>There ! is a 4" hole in the
center.>Coating>> is>> gold.>>There is a hand
drawn diagram of the test setup, but>> it>>
doesn't>really seem to convey much information
about the>> mirror>> itself.>>There is an note
about thermal cycling as part of>> a test:>>>
Thermal Cycle> Liquid Nitrogen to +350 F> 3 times>
1)>> Incoming> 2)>> Post nickel plate> 3) Before
gold plate>>It was made>> by Applied>> Optics
Center Corp in Burlington! , MA for GTE>>>>
>Sylvania.>>_______________________________________________>ATM>>>>
mailing list http://www.atmlist.net/>>>>>>>>
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