Re: [ATM] Glass for flats

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

Kind of depends upon what you want for accuracy for the flat.  If you're
building a large flat for testing optics, a 1/10th wave flat can do you
fairly well.  Plate glass will do that without any problems except the need
to let it set where it is for a while to get the glass in equilibrium with
the air.  Pyrex is a lot better in this regard and you can do a 1/20th wave
surface on it.
For thickness, I'd go with at least 1/8th of the diameter to insure that the
glass doesn't potato chip on you on the test stand.  It will also allow for
a 3 point support when laying flat.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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