Re: [ATM] Computing surface from Ronchi image?

[Jim Burrows <burrjaw@earthlink.net>]

There were a couple of suggestions that it might be possible to quantify 
Ronchi by running it like LWT with a pinstick on the mirror.  I ran 
DIFFRACT to simulate a Ronchi test with 4 lines/mm (~100 lines/in) and a 
pinstick on the mirror.  The diffraction, which messes up Ronchi, also made 
the pins almost disappear.

It turns out that diffraction helps LWT (with a single wire) - the centered 
pin actually lights up - an application of "Poisson's bright spot".  John 
Swenson says he observed this in a real LWT.

         -- Jim Burrows
         -- mailto://burrjaw@earthlink.net
         -- http://home.earthlink.net/~burrjaw
         -- Seattle N47.4723 W122.3662 (WGS84) 

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