Re: [ATM] Another Astigmatism question, but at the sphere stage

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

If you properly rotate the mirror and lap, you shouldn't get any
astigmatism on the mirorr.  Ronchi will show astigmatism better
than Foucault will and you have to look for the right angle to
see the S curve in the lines.  If the stig is vertical or
horizontal you won't see it as it will be hidden in the results.
Turning the mirorr by 45 degrees will show it up very nicely if
there is some there.
I'd start parobalizing again and not worry too much about the
astigmatism if you polsih right.  The star test is really the
true determinant of stig and then only on a bright star where you
notice that the star image can be made oval at two spots in the
focus range with the axis of that oval changing with the focus
change.
Bob May
bobmay@nethere.com
http://nav.to/bobmay
http://bobmay.astronomy.net

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