[ATM] Re: Second Thoughts on Mirror Support

[stuart452 at earthlink.net (Stuart Hutchins)]

Jeff,

I agree, and I'm perplexed.  There are a lot of people gluing down mirrors,
and a lot of people saying it can't possibly work.  Glass bends if stressed;
we can see the degraded star images. Kinematics and whiffle trees are the
long proven principles to restrain the optic with negligible stress.  But
RTV has got a lot of adherents (ooooohhh, a pun!) and I for one have not
seen any analysis for typical cells that really shows what the stresses are.

Mark's cell's show  Strehl ratios over 98%.  A mirror maker is happy to get
into the 90's for a base figure.  Maybe we can't readily see the effects of
some of these mountings when the optic is more than 1/8 wavelength.

I still think your approach is the right way model the problem, whatever the
answers turn out to be.  It'll be good to know just how far RTV complies
with good telescope making. (oooo-oooo-hhhh, another pun, *%&$. time for
bed)

Stuart


----- Original Message -----
From: "Jeff Anderson-Lee" <jonah@eecs.berkeley.edu>
To: "Stuart Hutchins" <stuart452@earthlink.net>
Cc: "Mark Holm" <mdholm@telerama.com>; <atm@atmlist.net>
Sent: Thursday, February 05, 2004 3:31 AM
Subject: Re: [ATM] Re: Second Thoughts on Mirror Support


> Hmm.  If that truly is the case, I would not expect Don's Discovery
> mirror cell to work--but it does!
>
> In such a case, a 2.7e-4 inch bend would cause a 153lb differential
> between the inner and outer support points which would undoubtedly warp
> the mirror.