AF-S is only applicable to Nikkor lenses that came to market in 1996 and after. These lenses focus with their own built-in auto focusing ultrasonic Silent Wave engine, instead of the focus drive motor in the camera, making for lightning speed focus acquisition. Most useful for fast-moving subjects. The first were the 300mm f/2.8, 500mm f/4 and 600mm f/4, all D ED IF AF-S lenses. AF-S lenses with a “II” designation weight less and are generally smaller than their equivalent predecessors.