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>Does anybody know what a C or C/S mount is and whether there exists
>an adaptor for M42 threaded or other lens types?
"C" mounts are a standard (thread) mount for 16mm movie cameras.
Nikon (maybe others) made an adapter to mount 35mm format lenses
on 16mm movie cameras, but as far as I know, no one made one to
go the other way around. You could probably make one starting
with a "T" mount for your camera and a little ingenuity (I adapt
enlarger lenses to Nikon mount using reverse adapters.), but C
mount lenses will not focus to infinity, or cover 35mm film
(unless it is used as a macro lens) on 35mm camera bodies.
Hope This Helps