Re: [ATM] Astigmatism in round robin mirror C with Foucault.

["Nils Olof Carlin" <nilsolof.carlin@telia.com>]

One way of doing a feasibility test is to use Jim Burrpows' Diffract to
simulate the test in question - it will allow quite a variety of
possibilities, and simulate astigmatism (wish I knew what those Zernike term
suffixes mean ;-) and see what happens - with a certain RMS value (shown) of
astig, and the axes aligned where they should be, if you can't detect astig
in the simulation, you are not likely to do so in reality.
It seems to me that the "steel ball" test of Texereau (p 86 in my edition)
may work for a spherical mirror, but is essentially useless for any
practical paraboloid.

One method that might work, I believe without having tried, is a Foucault
test with a Couder mask with 2 rows of openings arranged in an "X" fashion -
you match the diagonally opposite openings of each arm (make top and bottom
of each opening "horizontal", i.e. at right angle to the KE). If astig is
present, the readings along "/" and "\" directions would differ, and
hopefully you could use sixtests to get the difference of radii with
reasonable precision, although a little less than with a conventional test -
repeating this after turning the mirror, hoping to find the position where
the axes of astigmatism are aligned to produce the maximum effect.

Anyone with a known astigmatic mirror lying around?

Nils Olof

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