Re: [ATM] Blank ratios for different materials.

["Bob May" <rmay@nethere.com>]

Actually, the debat over ratio is more complex.  Smaller mirrors
dno't have the weight of the larger mirrors so they can actually
be made thinner than larger mirrors.  I've seen a fair number of
12.6" porthole mirrors that were three quarters of an inch thick
turn into nice tenth wave or better mirrors and they all were of
a typical difficulty in figuring the mirrors.  I did occasion
ally note some "potato chipping" of the mirror on the test stand
but rotating the mirror by forty five degrees showed that the
mirror was just bending.  Interefrometry would show that up and
would also show that the problem would not rotate with the
mirror.
\I would say to check with PL(OP and see how thin you can make a
mirror and not exceed the tolerance for induced error from the
mounting for a 2 point mirror cell.  If you're happy with a
twentyth wave of induced error, then that will define a ratio for
that diameter of a mirror.
Bob May
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