Originally posted by ronnies Interesting as my ST701 has a plain M42 mount with nothing to connect to a tab on the lens.
Ronnie
I don't see exactly what the tab on the lens is engaging with on the mount of my ST605N either, but the tab is definitely on the lens, which undoubtedly came with the camera originally.
Mamiya-Sekor SX lenses are also screw mount with an extra little pin, and also a rim on the back end of the lens mount. If I put the 200mm one of them I have on my Pentaz ESII, the rim is well outside of the circumference of the camera's slightly protruding mount ring, and so is the pin. Neither interferes with mounting the lens properly. Yet the rim and the pin both interfere with mounting the lens fully on a Pentax DSLR with it's m42-to-K adapter. The pin wouldn't be hard to remove, but it would take a couple of hours (or more) of filing to get that rim off, so it will remain a film camera lens.
Anyway, next roll of film I put through the ST605N, I'll also try a couple of old Takumar and other m42 lenses and see whether the camera does anything different with tabless lenses.