Quote Originally Posted by OldBodyOldSoul View Post

I guess I'll be on the lookout for a Spotmatic then. One question, possibly of the dumb kind: These lenses have a pin next to the rear element that stops down the lens. Do all M42 cameras use the same principle or do I have to pay special attention to that area? I am not necessarily opposed to testing these lenses only wide open, but would like to know that in advance. EDIT: Now I see that not all lenses have the pin... more reading on M42 mount is in order.
Most later M42 cameras work with that pin-actuated diaphragm mechanism. (Spotmatics, ect...). Earlier ones don't.

Be careful as some M42 cameras designed to allow full-aperture metering (Spotmatic F, Pentax ES, Fujica 801, maybe some Mamiyas) can't mount some lenses properly (the 25mm Flektogon being one, at least on the Pentaxes and Fuji).
No problem with other "plain vanilla" Spotmatics and other M42 cameras.