Re: [ATM] testing an f/2.6 mirror?

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

Then there's always a bit of spider silk!  In this case, any old
spider silk will do just fine.
The interesting thing in this test is that the slit needs to be
finer than the wire.  The shading is from the blocking of the
light from the slit to the eye and a slit too large makes for a
very faint shading.  Another way to look at this test is that it
is a double slitless Foucault test.  The depthy of the dark ring
on the mirror is from the amount of light that is blocked by the
wire.  The test is a lot easier to evalusate because there is a
ring produced on the miiirror rather than trying to evaluate two
holes for a shade of gray that are far distant from each other in
angle.
Bob May
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