My original question is basically a theoretical exercise for fun. I obviously know the AIS lens won't meter, I just want to know what crippled it. As has been stated, the Ai tab is the culprit. Ok, let's go from there.
Originally Posted by PhotoJim
After I posted the original question I took a further look at the lens mount. Again, what I am after is trying to determine if the body could meter at all with a AIS lens set at minimum aperture and what that determining factor is.
PhotoJim is right in the respect that the Ai tab, which is at the 1 o'clock position on a N90, is the determining factor in manual operation with a AIS lens; Outside of telling the camera that the lens is set at the smallest aperture for operation in the program modes. I do not know the extent of program operation with a AIS lens. I believe it's restricted.
The N80 body on the other hand has a lever at approx the 7:30 position that tells the camera that the lens is set at the minimum aperture. A AIS lens will make that contact. So with that in mind, and the fact that the Fee warning doesn't disappear on the N80 with a AIS lens set at minimum (in this case F22) what the camera is apparently seeking is a response from the AF chip. My question is, what that response is.
If you go to this link you'll see Fig 17A which shows the 5 pin out of a earlier Nikon body like the N80
So on this diagram 1a is power and 1e is common for AF focusing and maybe for power to the chip. I'm questioning what b, c and d are. I'm not big into electronics, but I generally thought "C" serial clock times a response. "B" and "D" I have no idea. Generally thinking "B" or P1/P2 is a switch or a path for Auto focus. I'm thinking the thin film board sends a signal to P1 and looks for a response from P2 such as circuit is closed or maybe AF focus is attained, although I thought that was a body cell determination. "D" is a question. Maybe someone here with knowledge in electronics can entertain some idea?
I know that at one time someone was chipping the AIS lenses. Since they are manual focus, the chip could only pass a signal. I don't think it would be a focus signal cause how do you fix that. It would just have to be perhaps a aperture signal. Not having a trashed AF lens to dissect I can only conjecture that it is a electro-mechanical switch, or a tab in the lens moves a lever on a switch. Who know's.