The Nikon Nikkor 28mm f/2 Ai-S is a wide-angle fast manual focus prime lens for 35 mm Nikon F SLR cameras.
As compared to the previous versions, its closest focusing distance is slightly reduced, and correspondingly its max. magnification ratio is a bit higher.
The optical scheme of the lens includes 9 elements in 8 groups. The same optical formula is employed by the Nikon Nikkor 28 mm f/2 versions:
1975-1977 - K version (SN 335001-347733)
1977-1981 - Ai version (SN 450001 - 454838 and 540021 - 565127)
1981-2005 - Ai-S version (SN 575001 - 619716)
К (1974) - a new type with exterior, resembling Ai lenses, but functioning as previous types. It has a rubberized focus ring, but with finer texture than that of Ai lenses. It has no ADR scale on the aperture ring, no second diaphragm designation in the rear part of the lens, no aperture scale. The reason of such labeling of this lens type has not been revealed.
Ai lenses (1977) feature auto indexing on the aperture ring to transmit information to the camera. The aperture ring with the second ADR (Aperture Direct Readout) scale is visible in the viewfinder of Ai cameras. The prongs have cut-outs in them to help illuminate the f/stop markings for ADR. There is a coupling ridge on bottom of aperture ring. PC and reflex lenses have no automatic indexing, but are labeled with the Ai index to designate the lens body type.
Ai-S (1981) - Ai lenses with shutter-preferred mode (S for Shutter). AI-S lens' minimum aperture is marked in orange on the aperture and ADR scales. It features a linear aperture control by means of the lever for a more accurate exposure adjustment in shutter- and program-preferred modes. There is a half-round cutout in the mount to identify Ai-S lenses.
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Posted by: dv Date of publication: 07.12.2012