Re: [APML] Star Roundness (was needed- an excellent sense of direction)

["Mike Cook, AF9Y" <mwcook@concentric.net>]

>From: Dave Rowe        	Aplanatic@aol.com
>
> in PS and I am not so sure about your two-corner-only observation.  I see a 
> bit of elongation in the center of the frame as well.  Isn't there a program 
> that the CCD folks use that will give us a quantitative evaluation of the 
> star's roundness in all four corners and the center?
> 

    Yes there is.  MaxIm provides a measurement of flatness:

"The flatness is an indication of how out-of-round the star image is. A flatness
of zero is perfectly circular, while a flatness of 0.1 indicates that the star is
longer in one dimension than the other by 10%."

     When everything is just right, I get a measurement of 0.02 or less at the
center and 0.08 at the extreme corners (due to the off axis astigmatism of
the AP teleconverter).

Mike



Mike Cook, AF9Y
http://www.webcom.com/af9y
mwcook@cris.com




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