Re: [ATM] Calculate Astigmatism

["Stephen C. Koehler" <koehler@securecomputing.com>]

Mike,

> Let's cut ourselves some slack and multiply that by a factor of 4. So to 
> measure primary astigmatism to even maximal tolerance we'd have to measure 
> radius of curvature differences to ~0.05mm. That might not be so difficult 
> *if* you measure two or more diameters without disturbing your apparatus. 
> But when you do a zonal test on a single diameter, rotate your mirror, then 
> fiddle the tester to relocate the light cone you're almost certainly 
> throwing away the ability to make differential measurements to the required 
> accuracy.

I don't understand the need to not disturb the apparatus over a mirror
rotation.  Couldn't you use the measurement of the center zone on each data
set as a baseline, or at least make the assumption that your innermost zone
is not much affected by astigmatism?  This would eliminate the need to
maintain the test rig distance over a mirror rotation.

Once the zonal readings are captured on multiple diameters, I would think
some 2D version of your modal fit using  a few orders of symmetric terms
plus the primary astigmatism terms would quantify primary astigmatism 
pretty well.
-- 
Steve Koehler
koehler@securecomputing.com


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