To: atm{at}shore.net
From: tkrajci{at}san.osd.mil
Reply-To: tkrajci{at}san.osd.mil


>From: "Jerry B. Hillman" 

>...1/8" of felt, on a 1/8" bed of silicone would give 100% support yet
allow
>the mirror to adjust to temperature changes.

I disagree, and recommend that you find a way to get air to the back face
of the mirror for better cooling performance.

However, if the mirror is very thin...less than half the thickness of other
amateur mirrors...you may be able to get away with cooling only the front
surface of the mirror.

I'd be interested in hearing of tests or field experience from folks on how
well a very-thin mirror cools/behaves when the back side is not exposed to
cooling air.

>...A sling would provide the edge
>support needed, as has been proven.

My concern with slings is friction/stiction.  Some sling users need to
jostle or bump the mirror cell because of the sling system.  That is a sure
sign that friction/stiction is at play.  Make sure your design and
materials don't allow this to happen.  Also, choose a sling that does not
change length with humidity/temperature.

>Perhaps I don't understand the significance of the point support system,
and
>I do use a six point support cell on my 10", but if the spacing is so
>critical, doesn't that lend to errors in support that would be avoided by
>thinking outside the box and trying for complete support.

Complete support may work...if you can adress cooling issues, and can show
that there is not too much stiction/friction problems with the entire
mirror laying against the cell backing and sling.

Good luck,
Tom Krajci
Tashkent, Uzbekistan

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