Canon 20D Backfocus?

Does anyone know how much backfocus is required for a Canon 20D to focus on a 20" F/5 reflector? Novaks' book Newtonian notes states the typical 35mm SLR needs at least 1 3/4" for the camera alone and typically more depending on the Prime focus adapter needed. Do the new digital SLR cameras need more or less backfocus than the older 35mm film cameras. Any help would be appreciated.

The 20D is an EOS camera. It uses EOS lenses, just as a film EOS uses. Therefore it is exactly the same backfocus as the film EOS cameras.

When you say how much "backfocus" does one need, are you asking how far from the lens mount to the ccd chip?

Alex