RE: [ATM] 'Commercial' annealed, rather than 'fine' annealed

[Mark Holm <mdholm@telerama.com>]

Here is a little bit of logic.

1. High quality annealing is slow, and therefore expensive.
2. Amateurs make up a very small fraction of the customers of an outfit 
like Newport.
Newport wouldn't bother to offer the higher grades of annealing just to 
satisfy the amateur market.  It just wouldn't pay.

Therefore, professional opticians, who work a lot of glass, and have a 
lot of experience as well as, in many cases, a good dose of book 
learning must be buying a significant amount of their glass annealed to 
the higher standards.  It doesn't seem likely that, with many, many 
years of experience in optical fabrication, the industry would be paying 
for an expensive option they really don't need.

Conclusion 1: Some optical jobs really do need highly annealed glass.

3. Well made ATM telescope mirrors actually have pretty tight surface 
tolerances, even by professional standards.  (The pros can do better 
when they really work at it, but it isn't often they really need to.)  
Thus, ATM mirrors are in the class of optics that need good dimensional 
stability.

4.  Bigger pieces of glass are both more likely to have annealing 
problems, and more likely to suffer appreciable surface distortion from 
the effects of poor annealing.

Conclusion 2:  Larger ATM mirrors are fairly likely to need good 
annealing in order to perform really well.

Mark Holm
mdholm@telerama.com

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