From: "Dwight K. Elvey" 
To: atm{at}shore.net
Reply-To: "Dwight K. Elvey" 


>From: "George Anderson" 
>
>A question about photographing with a fast (f/4) newt...
>If the film surface was curved like a film holder for a schmidt camera
>would this eliminate coma or would I just have clean sharply focused
>coma?
>
>George Anderson
>Montreal Canada


Hi George
 No, there would still be the effects of coma. You can
get a better focus with a curved focal plane that matches the telescope
that you are using. The issue with coma is that you are using a parabolic
mirror surface at an angle that isn't aligned with its axis. A Schmidt
camera with a spherical primary, sacrifices spherical aberation for not
having coma. By using an aperature stop at the ROC of the primary, you also
can get uniform illumination over the entire field of view( you do lose
effective size of the primary ). You also have to remember that film grain
size may be greater than the coma you are worrying about.
 There are coma correctors and field flating lenses that
can be added right above the film.
Dwight

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