From: "Jack Schmidling" 
To: 
Reply-To: "Jack Schmidling" 



From: "Mel Bartels" 

> No.  What you are saying is that any offset shadow or obstruction placed
> in front of the tube would magically produce coma when there was none
> before.......

Not quite but I will certainly do the experiment that  you suggested.

I suspect it has something to do with the fact that this obstruction is a
special case in that it is supposed to be at the optical center.

> Coma does not result from obstructions whether centered or not.  Coma for
> paraboloids is an off-axis issue, not an on-axis issue......

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.

js

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