Moon Angular Size
The Moon is roughly 1/2° (in angular width) from edge-to-edge. The Moon doesn't have a perfectly circular orbit ... it's a little closer or farther depending on where it is in the orbit. When the moon is at it's closest point (perigee) it appears to be a little bigger (it can be just fractionally larger than 34 arc-minutes wide).
Ideal Focal Length
Given a camera with an APS-C size sensor (1.5x crop factor), you might be able to fit the Moon into the frame with a focal length of 1800mm ... but that's a pretty tight fit and doesn't leave much margin for error. Around 1500mm would be a more comfortable fit.
Telescope Focal Length
You mentioned having an 8" telescope but you didn't mention which model. I'll take a guess that this is a Schmidt-Cassegrain Telescope (SCT) and not a Newtonian reflector since there are other issues using a DLSR with a Newtonian reflector (most are not well-suited to astrophotography with a DSLR -- but there are exceptions).
If true (telescope is an 8" SCT) then you probably have an f/10 telescope which would mean your focal length is about 2000mm ... that's a bit too much to fit the entire disk of the Moon.
Using a Focal Reducer
You can obtain a focal-reducer (depending on the specific telescope model it may or may not be a combination focal-reducer/field-flattener). Most of these will give you a reduction factor of around .7x (sometimes it's .65 or .68, etc. but it's probably at least .7 ... convenient because a .7x reduction also reduces the focal ratio of the scope by 1 full stop meaning it also doubles the collection of light. So your 2000mm f/10 scope becomes a 1400mm f/7 scope.
At that focal length (1400mm) you should easily be able to fit the entire disk of the moon in your camera's field of view.
Adjust the Exposure for use with Focal Reducer
Avoid over-exposing the Moon (don't trust the camera's metering). Your shutter should speed should be roughly half of your camera's ISO setting. e.g. if using ISO 100 then use a shutter speed of 1/200th sec. At ISO 200 set the shutter to 1/400th sec. etc. Evaluate the images and tweak as needed (you might need to shoot slightly faster to ensure nothing is over-exposed and you have good detail across the surface of the Moon.)