The stop-down mechanism that holds the lens at full aperture until the moment of exposure often sticks in a partially-closed position. This has resulted in over-exposed images. This occurs when manually pushing and releasing the lever off-camera or shooting on camera, as verified by looking through the lens with an open back.
The lens uses an Adaptall II to mate to my 1979-purchased Minolta XG-7. I suspect the Adaptall as the source of the problem, as the stop down works smoothly on the main lens by itself.
Has anyone experience similar?
My other 3 lenses and 1 doubler (Vivitar and Minolta) have never had this problems.
This is common after a number of years; lubricants thicken over time and turn into adhesives. If the problem is in the Adaptall mount, you're in luck: It's easier to work on than a zoom lens and there's no glass in it to mess up. You might try removing the mount from the lens and dripping lighter fluid into it wherever you find openings, then operate the linkages to work the lubricants out. If it doesn't work, it won't be any harder to disassemble and fix than it would if you hadn't given it a try.
