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Re: [ATM] astigmatism in star test

At 2004-05-18 20:02 -0500, Jerry B. Hillman wrote:

>The first star testing session yielded the fact that there is no visible
>astigmatism in my primary mirror, or the rest of the scope for that matter.
>Additional star testing will be done when the skies clear, but so far I know
>that Ronchi testing on a star yields straight lines edge to edge regardless
>of how many lines I have visible, all the way down to one.

Similar to Foucault, a Ronchi star test can't see primary astigmatism.  If 
the Ronchi grid is parallel or perpendicular to the astigmatism axis, the 
lines will be just as straight as a perfect mirror.  If they are at an 
angle to the astigmatism axis what you'll see is still nice straight lines, 
but slightly tilted.

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

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