Re: [ATM] 40" mirror

["Mel Bartels" <mbartels@bbastrodesigns.com>]

> this thread but it was recent , mentioned that Mel Bartels had a rule of
> thumb that a 4 inch thick mirror never reaches thermal balance .

The local club has owned a 16 inch cassegrain with 3.5 inch thick primary. 
It NEVER reaches equilibrium except for slow changing temperature summer 
evenings/mornings just before sunrise.  With active cooling, the time 
constant is much improved.

As far as equivalence of flexure, if takes as a unit of flexure=1, a 20 inch 
diameter mirror that is 2 inches thick, a 40 inch mirror will need to be 
EIGHT inches thick to achieve a unit of flexure=1.  A 4 inch thick 40 inch 
will have 4x the flexure of the 20 inch mirror.

Mel Bartels 

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