[ATM] Testing small mirrors

[Mike Lockwood <melockwo@uiuc.edu>]

Hi,

I am wondering what is the smallest mirror that can be accurately 
tested with a slitless Foucault tester - that is, a slitless tester 
with the light source and knife edge vertically separated by a 
distance I'll call Dv.

I ask because I make small test plates for Cassegrain secondaries, and 
because I was asked if I could make a small fast sphere of high 
accuracy.  I am curious what errors are intruduced by not having the 
light source and knife edge coincident.  If it is significant, I will 
need to add a beamsplitter.

Can anyone point me to a mathematical analysis that will allow me to 
calculate the error introduced by the light source and knife edge both 
being on axis horizontally, but separated (off-axis) vertically, if 
the the size and ROC of the mirror are known?

I can probably understand the math and I would like to see an 
analysis, but I'm not sure how to set up the problem.

I searched the archives and found this:
   http://astro.umsystem.edu/atm/ARCHIVES/FEB04/msg00519.html

but I don't think it quite answers my question, which has been asked 
before.  If it does, someone please enlighten me!

Is it possible that the solution is to use a Caustic-type test with a 
slit and wire?

	Thanks,

	Mike Lockwood


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