Originally posted by minimodi
On the back of the Mamiya lenses is a small pin that moves with the aperture ring - I thought that pin was "talking" to the camera and providing open aperture metering?
I wasn't talking about the aperture pin -- on SOME of the Mamiya lenses there is another tiny hard pin that can cause problems. Whether if you filed down the ring the normal open-aperture metering would work on a Spotmatic I have no idea -- I've only used them on modern cameras with adapters where the pin is not used in that way. If you want to do the work and do mind messing them up a bit, filing down the ring so it will mount flush is worth the effort (and removing that that other pin if present, which it is in that picture in the link you provided) -- those are fine lenses -- the 135mm is very nice indeed. I've modified several M/S lenses so I could use them.
Almost any other m42 lens should be usable, and most with an auto aperture pin should allow open aperture metering -- the other exceptions that I know of that might give problems would be some Fujinon lenses and some Helios lenses. And Yashinon DX lenses will mount, but may hit the mirror at infinity because they extend too far (the 50/1.7 and 50/1.4). But any Takumars will obviously work (very early models may not allow open aperture metering, but all the Super Taks and SMC Taks will), as well as old m42 Vivitars, Rikenons, Focal, Sears, Tamron, Sigma etc etc.