Ah, you may have the same problem I have with my RTSII. There is a stub on the back of the lens of the Contax MM/AE lenses that mates with a sliding lever that is inside the lens mount. When you mount the lens, the stub pushes the sliding lever to a set position, which tells the camera what the maximum aperture of the lens is, and hence tells the electronics what all metering readings should be relative to the max aperture. My RTS doesn't read the max aperture correctly, which throughs off all the meter readings. I suspect -- but have confirmed -- that the sliding lever motion is transferred to something akin to the famous variable resistance strip in Nikon FTn heads, which when the wear out prevent proper exposure. I had a repair shop try to fix my RTS II but no luck. Next I'll try Nippon photo service in NYC.