Ultra Telephoto photography is easily achieved with your telescope by purchasing this Celestron SLR Camera Adapter with Integral 2x Barlow Lens.  You'll need to take precautions to minimise vibrations, such as locking up the mirror if possible as well as using a cable release or remote control to fire the shutter.  This SLR adapter's got a built-in 2x barlow lens to assure that any telescope can achieve proper focus, but many telescopes will be able to use it with the barlow attachment removed if you prefer.  It will depend upon how much in-travel your focusing barrel has at its disposal.  It can, of course, also be used on a catadioptric scope which has a 1.25" focuser barrel.

First, remove the eyepiece. Next, attach the SLR camera adapter where the eyepiece would normally be attached to the telescope, and screw in a t-mount adapter to the opposite end of the SLR camera adapter. Now you can attach your camera to the t-mount and you are ready to begin taking pictures!

Note: Your camera will need to be in fully manual exposure mode, although some brands of camera may also work in aperture-priority auto exposure mode.  Additionally, if there is a switch on the camera which chooses the focus mode, that switch must indicate manual focusing.

Inserts in to 1.25" focusers

Requires T-mount SLR adapter (to suit your DSLR SLR - sold separately)

Incorporates 2x magnification

Built-in barlow lens can be removed (some telescopes will not focus properly without barlow)