Re: [ATM] How round and how square should it be (blank mirror)

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

The sides merely need to support the front of the mirror and can
be at about any angle.  Some people (and companies) build
telescopes with a cone shaped backside for light weight with the
edges of the blank being a lot thinner than the center of the
mirror.
As to roundness, the blank should be reasonably round so having a
blank that is 1" different in diameters is a bit much but you
don't have to go to 0.001" roundness to be considered round.
Grinding the front surface won't be affected by the oblateness of
the blank so don't worry about that.  The sole effect of being
oblate is that the Airy disk won't be round but rather oblate in
the same ratio as the difference in the mirror.
Bob May
bobmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net
Replace the obvious words with the proper character.

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