Re: [ATM] Can Foucault Results Indicate Astigmatism?

[Jim Burrows <burrjaw@earthlink.net>]

At 2004-05-13 22:25 -0500, Kurt Clement wrote:

>I am using TEX and Foucault Test Analysis 1c/Reifke, and they both 
>indicate that I am at 1/8 or better and 0.96 Strehl, using a three zone 
>mask.  Included in this message are the TEX results...

Sixtests agrees, surface RMS = 6.2 ± 2.8 nm (2 sigma, assuming .01" sigma 
readings), .98 Strehl.

>How would I interpret this data to indicate the presence or absence of any 
>astigmatism?

Essentially, the Foucault test is blind to primary astigmatism (it can see 
higher order astigmatisms, but they usually don't hurt as much as PA) - 
you'd have to measure the ROC for different diameters to hair's width accuracy.

>I sat down at the library and read parts of Texereau, edition 1, ...

About the only quicky PA test available to the amateur is Texereau's bench 
star test, p. 85 (edition 2).  It's not very good - non-passing PA is just 
barely visible (see http://home.earthlink.net/~burrjaw/atm).

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

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