Since it has no meter linkage, and no automatic aperture, on a camera such as the Df, which has a flip up AI tab, a preset lens will operate the same whether or not it's AI compatible, and unlike auto aperture lenses it also does not matter how the stop down lever of the camera works, since it will not do anything anyway. Compatibility just makes it easier to put on in a hurry, which is why I turned down the skirt on mine back when I was using it on an F3. When stopped down, it meters, and like any manual lens, will work in either M or A modes. The camera interprets the dimming when stopped down as lowered ambient light, and corrects for it. Mine meters quite decently in A mode on a D7100.