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

["Koehler, Steve" <Steve_Koehler@securecomputing.com>]

> I hope to post pictures of both the appearance of the mirror at null, 
> and the tilting of the line, if Dale can capture some good images.

Dale and I will attempt to get some good pictures this week of the appearance of
the astigmatism of mirror C under the holographic null test.  In case we are
unsuccessful, I have posted a simulation of what this should look like in:

http://www.atmlist.net/contrib/steve_koehler-at-securecomputing-dot-com/holonull
/holo_astig.jpg

As you can see, the shadow of the "knife" leans one way on one side of focus and
the other way on the other side of focus.  The best position to compare the tilt
is in the two pictures in the middle of each row.  The only thing I didn't match
to the actual test in this simulation is that I used .08 RMS of astigmatism,
which is probably a bit more than mirror C actually has.

In case anyone didn't absorb the discussion about the holographic null test from
December, this test uses your normal Foucault rig, with the restrictions that
the light source and "knife" must be narrow slits, and the light source must be
relatively  monochromatic (e.g., a red LED).  The only additional piece of
equipment is that you must cut out a paper mask of the proper shape.  (It took
me about 25 minutes to cut out the mask for the 6"
mirror.)

-- Steve Koehler
   steve_koehler@securecomputing.com


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