Quote Originally Posted by John Koehrer View Post
No it's not rocket science.
You don't want to accept that FF distance doesn't matter. For work with a bellows, yes the lens will form an image but not at infinity.
With the mirror down it will not allow the lens to be close enough to the film. Remember, the focusing screen in the camera is equivalent to the distance to the film plane.
Raise the mirror and put a ground glass at the film plane and it will work, otherwise no go.
John:

I think you threw one too many negatives into the phrase "You don't want to accept that FF distance doesn't matter." I think it should be "You don't want to accept that FF distance does matter."

And no one seems to be mentioning that the size of the opening in the camera also matters - just try to fit a Canon breech lock FD lens through a Pentax screw mount lens mount.