Here's the rundown...Originally Posted by DilbertJM
FM (1977) - there are two versions. The early model has a knurled collar around the shutter release. Both versions have a metal vertical shutter 1- 1/000 + B, X sync at 1/125th. No interchangable focus screens. Has a small button on the lens mount to lower the aperture follower to allow use of non-AI lenses. Shutter speed and f/stop readout in finder. 3 LEDs for meter indication. Accepts MD-11 and MD-12 motor. Motor does NOT power the meter in any of the FM series bodies. Data MF-12 back requires use of X sync terminal on front of body
FM2 (1982) - like the FM, but adds interchangable focus screens. Top shutter speed increased top 1/4000th sec, X sync at 1/200th. No aperture follower release button - we're in AI lens only territory here. Accepts the MF-16 data back with internal contacts, so no sync cord required.
FM2n (1983) - As the FM2, but X sync at 1/250th. Also available with titanium body parts.
All are excellent cameras.