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

["mbyorick" <mbyorick@starband.net>]

Art Bianconi asked (sorry, Art, I meant to hit the 'Reply All' button!):

>With only a 1 7/8" thickness, I'm curious about the cell design you
>expect to make to keep that thing from flexing.

According to my preliminary homework, I think that an 18 point cell
will, in fact, accommodate a 24" x 1 7/8" mirror, with an acceptable RMS
error.  For example, Jeff Anderson-Lee's fantastic PLOP-based mirror
cell analysis, at: 

http://www.cs.berkeley.edu/~jonah/18plus/


indicates that a 24" x 2" thick mirror should perform acceptably with an
18 point 'PLOP-compliant' cell (see, e.g., the graph at the bottom of
the web page).  Reducing the mirror thickness from 2" to 1 7/8" may make
the 18 point cell near-marginal, but a 27-point cell (which appears to
be overkill) could be used if a more specific analysis indicates that
better support is needed.  

As for 'fine' annealing versus 'commercial' annealing, your theory
basically makes sense to me.  However, being a pragmatician, rather than
a theoretician, I'm not going to worry about the theoretical
differences, since I haven't seen any data which would indicate that
fine annealing actually provides observable (a pun?) improvement over
the so-called 'commercial' flavor, in a real-world scenario.

Cheers,
Mike Byorick


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