The N80 would need to know the maximum aperture of the lens. It would get this value by communicating with a CPU lens. It needs the value for matrix metering as the matrix metering algorithm needs to know the absolute brightness of the scene. It also need max aperture value to display the aperture with its LCD. The F5 and F100 can't do matrix metering, P or S mode with AI-S lens but they can meter in CW or spot mode because their AI coupling tells them how many the stops the lens will close down when the actual exposure is made. The N80 doesn't have this coupling either so it can't do that either. It could do stop down metering if Nikon decided to do so but they didn't.