Nikon AI-S Nikkor series lenses

The AI-S line was created by Nikon in 1982 when the aperture mechanism of AI lenses was enhanced to feature automatic aperture control. This feature was to be used with cameras such as the FA, FG and F301 and allowed Program or Shutter Priority (FA only) modes to be incorporated into these cameras when used with AI-S lens. The AI-S mechanisms allows the aperture increments of an AI-S lens to be controlled more precisely by the camera than with an AI lens.

The orange-colored minimum aperture value marking, and a milled semi-circular notch in the bayonet ring distinguish AI-S lenses. The notch is designed to inform Nikon cameras that employ a mechanical automatic aperture control for different exposure modes, that lens with a linear aperture mechanism is attached.