Re: ATM Question on using the Ronchi screen.

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

Actually, the ROC for the Foucault test is normally done as a single
approximate value (1/4" is more than good enough) with the 3 values of the
Knife Edge being relative values from the ROC of the center zone.  Thus I
would read your results from the Couder Mask as being 0", .031" and .037".
I ran the numbers and saw that you have a 1/7.4 wave error of the surface.
Not all that bad.  You could do a little bit better but I would suspect that
the Ronchi grating test shows a sort of straight line in the center of the
mirror with nice round lines out from there?  If so, call it good as the
center, while it's off a bit, is mostly covered by the secondary anyway and
you won't be getting any reflections from that part of the mirror in the
part of the image where it counts most - the center part.  Now go out and
test the mirror on various stars and the planets and see how nicely it
performs.  After you are happy with that, go get it coated.
Bob May
My new web space address is http://webu.wigloo.com/bobmay/ or
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and my new email address is bobmay@nethere.com
Bob May