Cameras assume nothing. Simply put, if the OP just cranked the lens into place with no mechanical aperture linkage, the camera likely registers nothing--nada, aperture-wise. Old NAI Nikkors have to be updated to catch the AI tab to tell the body the aperture setting. Using them as you would with an adapter on a non-Nikon body isn't really on because of the potential to f-up the AI tab. Why all the confusion? Not all F-mount lenses are the same.