ScopeStuff’s SLR Lens to T-Thread Adapters offer adapter bayonets onto the back of your Canon EOS lens and presents male M42 T-threads. (M42 x 0.75mm for astronomy gear, not M42 x 1 mm “Pentax threads” common in the camera world.)
As Jim Henson at Scopestuff notes, “The adapter is as short as can make it to allow focusing with almost any camera format, with the focus plane about 18mm from the back face of the adapter.”
In many cases extender rings or spacers will be needed to get the right focus range for your setup. Common 1.25″ eyepieces focus with about 29mm setback. The Meade DSI (with ScopeStuff DSIF Low Profile T-thread Faceplate) focuses with 15mm of extension. C and CS Mount cameras should work fine, and they will test those and provide the numbers and suggested adapters.
Jim also adds, “With no space to work with, the bayonet lock isn’t a fancy spring-loaded button. With the adapter installed on your lens, you tighten a setscrew with a nice dog-tip that securely locks to the lens without marring lens parts. Allen wrench provided! Aluminum and ABS components, steel springs and screws.”
And a Nikon version is in the works. They are working on the version on which they comment, “what a strange lens interface!”