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


> From memory the distance from shoulder of the cell to the film plane is
> about 3.57 inches.......

You have a lot better memory than I.

I sort of gave up on using it on the 4" but am going to use it on the
16" again.   I quit using it when I switched to CCD thinking that the
field was
so small, it was not necessary.

Now, I am contemplating making a new astrograph and doing an F5 instead of
F4 to solve the coma problem.

How do I calculate the coma free field based on focal ratio?

js

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