Re: [ATM] Astigmatism

["Mitchell R" <funnybone101@embarqmail.com>]

Can't have your cake and eat it too!
One thing is to regularly move the glass about on the turntable
so that it never gets to the point where the oddities end up
getting strong enough to matter.
With coarse grinding and even most of the fine grinding, don't
bother to do this as the shape is constantly moving about each
time you're putting the glass down for a grinding session.  In
addition, the amount of glass being removed at the larger grits
is so much that it swamps out the errors being ground into the
glass by the poor support.  I'd be more particular when it comes
to the last grit before polishing to gain a better spherical
surface.  All during polishing you will be wanting to regularly
turn the glass on the turntable so that astigmatism doesn't show
its ugly head.
Another thing with thin glass is that you have to properly
support it when testing or you will be seeing a lot of bending of
the glass which you will misinterpet as being actually in the
glass surface and thus will try to get rid of it, finding that
either you can't (because it isn't in the surface) or polishing
in the error!
Hope this makes things a lot clearer for you.
Bob May


Hey Bob, thanks for all the mirror tips!

Have you cake and eat it to? Of course I want to! What the heck good is cake
if I can't eat it? ;)

Mitchell

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