[ATM] Auto Collimation Flat - not cored

[William Marriott]

Hello;

So, I have found in our optical shop, that you can
edge, core, slice up, stable material, with out
affecting the figure, though right next to the core
you might see a very narrow band affected, but, gring
the back, and sometimes fine, some times major
springing of the figure.

BIll Marriott
VA Optical Labs




--- Dominic-Luc Webb <dlwebb at canit.se> wrote:

> 
> I reported years ago (about 10-12 or so) that my
> full
> thickness pyrex 8" F/8 accidentally turned into a
> flying
> saucer when it fell out of its cell, and rolled down
> the
> tube. I lifted the front of the tube trying to keep
> it
> from ending up on my hard concrete floor. It had
> already
> rolled farther than expected, and my lifting ended
> up
> catapulting the mirror right out of my balcony. It
> nonetheless
> hit concrete, way down on the road below.
> 
> What to do at this point? Well, I quickly decided to
> savor the
> moment and enjoy watching the flight of the only 8"
> F/8
> parabolic flying saucer I am likely to ever see.
> After some
> moments of collecting my thoughts and realizing I
> now had an
> excuse to make another mirror (yippie), I went down
> and fetched
> it. Amazingly, only a chip on one side was lost. I
> still have
> and use that mirror, although, I am quite sure the
> figure must
> have changed considerably. I have no before and
> after pics
> of the figure for comparison, but I am sure I would
> not have
> aluminized it with the figure it currently has. I
> could be
> made to believe that a hole, or a crack, etc can
> change the
> figure of a flat.
> 
> However, I also know that manufacturers of glass
> filters produce
> large precision flats that are cut into the desired
> sizes. I am
> told these are very large sheets and many disks are
> cut from a
> single sheet.
> 
> Dominic
> 
> On Thu, 9 Aug 2007, Francis J. O'Reilly wrote:
> 
> > Shane,
> >
> > Have you considered the use of a beam splitter for
> the autocollimator? I would be hesitant to core a
> perfectly good flat. My concern would be that
> cutting into the surface of the flat would release
> stresses in the glass if there are any, and I
> believe that there usually are even in the most
> finely annealed glass, and cause a change in the
> surface. A beam splitter will allow part of the
> light to be reflected at ninety degrees for your
> viewing (or photographing) and analysis.
> >
> > Hope to see you at Stellafane this weekend.
> >
> > Francis J. O'Reilly
> > _______________________________________________
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> >
> 
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