Lots of people do medium format photography -- but the problem is that many telescope types either do not illuminate (ie have a large enough image circle) to cover a medium format negative. Some of the Takahashi and Astrophysics scopes (among others) will all or most of a 6x7 negative.

The previous post was a little misleading -- a 4" F/6 refractor will image the same way with a 35mm camera or a 6x7 camera attached -- one just covers a larger area. Some of the things that affect the way a photo will turn out, *independent* of the film format behind the lens are:

1. Aperture (ie, diameter) -- the larger the diameter, the more quickly *stars* are recorded -- since they are approaching point images, the area discussion is not really relevant

2. Focal ration (ie, F/Number) -- the smaller the number, the faster that *extended* objects (ie, galaxies, nebula, etc) are recorded. Unfortunately, this also means the faster light pollution is recorded.

3. Contrast of the optical system -- stray light leaks into all optical systems -- the better dark painted, baffled, tube extended, and/or flocked you are, contrast will go up, recording fainter stuff.

Sorry for the hurried description, but I was out of time.