Re: ATM Astigmatism on 20 inch thin mirror

["Vladimir Galogaza" <vladimir.galogaza@zg.tel.hr>]

>.  The thing that has to be
>considered is that the glass is very thin so you are going to have to make
>sure that the glass is properly supported or you will just put a the
>astigmatism back in in a different orientation.

How to properly support the blank?

Would it be proper to make a very thick disk from dental stone
(extra hard variety) or cement, say 2 or even 4 inches thick
than after cured put on it  a fresh layer of dental stone sufficiently thick
to accommodate
unevenness of the blanks back and put blank on it. Dental stone will
presumably
take the exact form of the mirrors back ( this is what dental stone is used
for by dentists)
 and when cured will  simulate thick mirrors stiffness ( to the point).

Now I ask experts to tell us what stiffness ( if any) will have this
composite
expressed in  equivalent thickness of some hypothetical pure glass blank.

Of course this composite will serve only for  grinding, polishing, figuring.
Later thin mirror should be separated and placed in one of those
multihundred point cells.

Regards
Vladimir.