From: Mel Bartels 
cc: atm{at}shore.net
Reply-To: Mel Bartels 


> I understand but explain this then....
>
> A defocused star that shows the diagonal shadow in the center of the star
> image, shows no coma when brought to focus.  All stars that display
> off-center diagonal shadows display coma when focused that exactly
> corresponds with the off-center position of the diagonal when defocused.


But they *do not* - not for stars on-axis.  Where did you get this idea?
There is no coma for on-axis star images, no matter the shape of the
aperture - obstructed, crazy-8, whatever.  Try the moving obstruction
experiment I suggest and see for yourself.

Mel Bartels

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