From: "Tom Krajci" 
To: 
Reply-To: "Tom Krajci" 


From: "James W. Burrows" 

>In good ol' shadow-matching Foucault, non-uniform illumination would
>certainly introduce errors - the difference in illumination would
result in
>a longitudinal reading shift to balance the zone brightnesses....

This is one reason I favor the wire test...it does not suffer as much from
non-even illumination...which is more and more difficult to achieve when
testing faster optics.

The wire test uses position of shadows, not comparison/matching of
brightness of separated shadows.

As your optics get faster, the wire test has more strong points in its
favor.  Also, compared to the Gavoila/caustic test...the wire test only
needs to measure longitudinal motion...so you can use the same traveling
stage as you do for the Foucalt test, instead of making a more complex
two-axis stage for caustic testing.

Tom Krajci
Tashkent, Uzbekistan


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