There is a pin or lug at 7 o'clock on the mount of all AI-S lenses (looking at the lens from behind) which Nikon calls the maximum aperture indexing pin. Only the FA and F4 (I believe) use this pin to obtain the lens' maximum aperture. However, my AI 55mm Micro has this pin and I am wondering when it appeared in production. Any manual focus AI (not AI-S) lens owners who would be willing to examine their lenses for presence of this pin, please tell me whether your lens has it, along with serial # or year of manufacture and focal length/speed. I will report back to the list as to how early Nikon started preparing to offer Matrix metering, because that is what the maximum aperture indexing pin is for I believe. Michael
