Re: ATM Autres follies de Foucault (More Foucault Follies)

[Mel Bartels <mbartels@efn.org>]

I too went through the same tortures with the Foucault test always being a bit
'off', particularly on fast mirrors.  I always figured it was me more than
anything systematic wrong with the Foucault.  Last year we had a long thread
where at least one person claimed that they could get within 1/30 or better with
the Foucault.  If you look at  a 6" f/8 or 8" f/8 and are very practiced, I
think this is not out of reason.  But when you start talking 6" f/4 or 12" f/4
or 20" f./4 or 40" f.4, then the Foucault test starts to disappoint.

I switched to the poor man's version of the Caustic test and that helped a lot.
For very large very fast mirrors Dan Bakken has shown the wire test to be most
effective.

But the star test is the most sensitive particularly when the mirror exhibits
bit a single error or two, so I always finish up with it.

--
Clear skies, Mel Bartels
http://www.efn.org/~mbartels