Re: [ATM] Is this Sphere good enough?

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

Yeppie, you don't need to start from a sphere although it does make the
possibility of attaining a good parabola a bit easier.
You are somewhere between a parabola and a sphere with that surface that you
have so it is just a matter of polishing down the high spots without digging
the center any deeper.  A bit shorter stroke should take that ring down
without any problems.
i try to get the guys to have something approximating a sphere as the need
for repair strokes is a lot less than otherwise.  The parabola is a
relatively unstable figure to hold so it will be taking of short sessions of
maybe 100 strokes until you get to the 1/4 wave level and then even shorter
sessions of polishing after that to gain the 1/10 or better surface desired
for an excellent mirror.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net


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