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Re: [ATM] 40" mirror

Jerry B. Hillman wrote:

>>Also consider a thinner mirror.   Four inches of glass will almost never
>>come to equilibrium.
>>    
>>
>I thought that is why pyrex is the substrate of choice.  Low thermal
>expansion coefficient.
>
Pyrex *is* lower than plate glass, but it's not zero.  (For that you 
need zerodur, astrosital, and the like.)  Also as others point out you 
get heat haze off of a warm mirror.  The new technique for dealing with 
this is to blow air over the FRONT surface of the mirror while observing.

Jeff



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