Re: [ATM] what is strelh ratio and how do I mount the spider

[Jim Burrows <burrjaw@earthlink.net>]

At 2004-07-27 13:45 -0400, David  Williams wrote:

>I heard a lot about the strelh ratio and I have wondered what that is.  Is 
>that something like the wavefront error measured in lambda, but just 
>slightly different?

It's spelled Strehl (real person:  K. Strehl, "Z. f. Instrumkde.", 22 
(1902), 213) ratio.  It is "the ratio of the light intensity at the peak of 
the diffraction pattern of an aberrated image to that at the peak of an 
aberration free image..." (W. J. Smith, "Modern Optical Engineering", 1966, 
p. 311).  The optical literature pretty much agrees it's the best image 
evaluation criterion, and a (good) estimate for it can be obtained from ATM 
mirror tests.

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

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