Aperture-setting prongs retained for backwards compatibility. The semi-circular notch on the lens mount. Linear aperture control means every millimeter movement of the aperture coupling lever corresponds to an equal amount of aperture stop-down. Similar to the mount on AI-S lenses except that the aperture prong is omitted. Introduced as less expensive lenses for a beginner's camera.
Lenses are typically single coated versus multi-coated.
AF Aperture prong is omitted. Incorporates autofocusing mechanism. Similar to AIS mount. Since 1988, all AF lenses have been fitted with a broader focusing ring to improve manual focusing. The new D-series transmits distance information from the lens to the camera body.