Quote Originally Posted by Lee L
Edit: just saw the last post, and the reason for the odd mm sizes is that the mounts were specified in inches IIRC. I believe the C mount was 1 inch x 32 tpi and the D mount was something like 5/8 inch, but I don't recall the thread spacing. But my memory may not be too reliable, so check good sources.

And I just found this: A C-mount lens produces a focal plane 17.52 mm behind the camera's flange, and a CS-mount lens produces a focal plane only 12.52 mm behind the lens flange.
Both C and D mounts have 32 TPI. The D mount is 5/8 inch. I use the old series adaptor rings to reverse mount movie and enlarging lenses on 35mm and LF cameras. A series 6 or 7 retainer ring epoxied, thread outward, on a lens board or body cap, can be used with step-up rings for about any size lens. Some old camera stores have boxes of adaptor rings hidden away somewhere to mount the lens on the retainer ring. The effective f/number is quite high with movie lenses reverse mounted for micro work. Thus, diffraction limits resolution, even when wide open.