Re: [ATM] astigmatism in star test

[Guy Brandenburg <gfbrandenburg@yahoo.com>]

I have seen astigmatism in a ronchi bench test. It
showed up when one end of the lines was fatter than
the other. We rotated the mirror by 180 degrees, and
you could see that the fatter end of the lines had
rotated by 180 degrees. Also, if you rotated the
mirror by other increments, the ronchi lines looked a
little bit  like the letter S. 
With some serious work, the maker of the mirror was
able to fix it and ended up with a very fine mirror
indeed. However, I was not able to do a startest on
it.
Guy B

--- Jim Burrows <burrjaw@earthlink.net> wrote:
> At 2004-05-18 20:02 -0500, Jerry B. Hillman wrote:

> 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.
>

=====
Guy  BrandenburgWashington, DChttp://home.earthlink.net/~gfbranden/GFB_Home_Page.html


	
		
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