Is anyone able to identify this bayonet mount? I've looked at every reference I could find and can't identify it. It's a modified or adapted M42 lens. I'm wondering if it can be undone, restoring the M42 without extensive work.
My wild guess is a 35mm movie camera mount. But really, I've never seen anything like it either. Is it a fixed mount or just an adapter screwed onto the M42 threads?
OK, looked at the post again, sounds like not an adapter but a modification.
It looks like a Pentax 20mm F4.5, the mount looks like it can lock in with any of the four tabs. It could be custom- like used in the scientific field. Was common to modify off-the-self lenses with custom mounts.
If the M42 thread had been modified or removed you'd need some screws to hold the alumium part in place and there aren't any. It may be the threads tight as it's a on off.