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Some clarification on astro-photography methods with DSLR and telescope:
1. Piggyback: Camera with lens rides on top of telescope using suitable bracket with 1/4-20 screw for camera. Great for wide field photography.
2. Prime focus: Camera without lens is attached to the telescope. The telescope is the lens whether it is refractor or reflector. First a T-Ring that matches your camera body must be used. The T ring converts your camera body bayonet mount to T2 female thread. Then a T2-adapter that has a T2 male thread screws into the T-ring. The other end is either a 2" nose-piece that slips into the focuser. (1.25" is also available but will vignette with cameras with larger sensors). e.g. if you telescope is 200mm dia./f5 then you have a 1000mm f5 telephoto 'lens'.
3. Eyepiece projection: The camera with lens removed and T-ring added screws onto a special eyepiece projection adapter. This adapter holds an eyepiece inside and the focal length of eyepiece and distance to film plane determines the effective focal length of the system. This method was popular in the film days for photographing planets and close-ups of the Moon. It is not used much anymore due to video astronomy offering far better results for planetary and Luna. Some eyepiece projection adapters were variable with a sliding upper body. Note only small narrow body 1.25" eyepieces with a short upper section could be used with this method.
4. Afocal: The camera with lens is placed via a suitable bracket (or hand held if steady enough for bright objects) in front of the eyepiece. The eyepiece used is typically 32 to 40mm or so with good eye relief to avoid vignetting. The zoom feature of the camera can be used to enlarge the object. Again this method is best for the Moon and planets and using small compact digital cameras.
Note I've not seen a Skywatcher Newtonian focuser but from what others have said it appears that it has a T2 male threaded adapter. It is also possible to get a 2"-1.25" adapter with T2 male thread. However I particularly do not like these as you could easily damage your field lens on say a 2" Nagler if you happened to forget to remove the 2"-1.25" T2 threaded adapter from the focuser.
Note often the problem with prime focus on a standard focuser is that you cannot rack in enough and hence the need for a low profile focuser, (or first try and release the primary mirror springs all the way and then tighten only enough to get collimation). The Skywatcher system overcomes this with a different design. I have a Tectron focuser with two upper bodies; one visual standard rack & pinion and then another photographic for prime focus photography. You simply undo two nylon screws, remove the visual and add the photographic body to get the camera much lower. This focuser is not made anymore that I know of.
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