In short, the whole scope acts as a huge telephoto lens. I was quite pleased with the results as this was my first attempt at prime focus photography. The full moon is probably a good subject to photograph for your first prime focus shots as the moon is so bright you only need short exposures. Short exposures mean sharper images with less chance of trailing taking place. Prime focus lunar photography can be done through most any scope provided it has a rigid, clock driven mount.
Polar alignment can be less precise related to the fraction of a second exposures.
Be warned, if any drift occurs related to overly sloppy alignment, this will result in blurred or less than sharp images. Another consideration is balance as mounting a camera on the back of a SCT or on front of a reflector can result in the scope being back or front heavy. Several good books give details and exposure times for prime focus astrophotography. I found Astrophotography for the Amateur by Covington, M . to be most helpful. In the end, it seems that polar alignment and tenacity are the two most important considerations.