Re: ATM Astigmatism on 20 inch thin mirror

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

No need to go so far back as 600 grit.  The last grit should be more than
enough to get to a good spherical surface.  The thing that has to be
considered is that the glass is very thin so you are going to have to make
sure that the glass is properly supported or you will just put a the
astigmatism back in in a different orientation.  If the polishing is what
did the stig. then you should be able to get it back out again with
polishing.
Since you have a machine to do the hard part of the work, just let it do the
work and watch it.
Bob May
http://nav.to/bobmay
bobmay@nethere.com
NEW! http://bobmay.astronomy.net