Hmm - depends on the size of the telescope and what you want to do with it. If you are talking using it a prime focus, then I'd say 4x5 is unlikely - in general off-axis aberrations increase rapidly and most telescopes are not designed to cover more that a 35mm frame. If you want to do some kind of eyepiece projection photography, then 4x5 becomes a possibility as you are enlarging the prime focus image. It then depends on the size of the telescope. Telescopes have a theoretical maximum magnification that is determined by the diameter of the objective. Generally this maximum is 50x to 60x per inch. For example a 10" objective has a theoretical maximum magnification of 600x. So the question now becomes, if I use eyepiece projection to enlarge the image to cover 4x5, have I exceeded the maximum magnification of the telescope.
A while ago I considered trying to take a picture of the moon on 4x5 sheet film with my 6" newtonian reflector. However after some quick calculations, I determined that for an image size of 4" for the moon, I'd need at least an 8" diameter telescope - and a 10" would be even better.
Can you give some details on the telescope? What kind - reflector, refractor, of Cassegrain? How big is the objective?
Dan
