BetterPhoto Q&A
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nikkor lenses

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February 23, 2001

First, the Nikkor AI and AI-S lenses are all manual focus.

The AI lenses were designed for manual exposure bodies with Photomic meters in the prisms for metering TTL. AI = Auto-Indexing, a feature which coupled the lens to the Photomic prism meter automatically (see the note below).

AI-S lenses are designed for Shutter Priority or Program Mode auto-exposure bodies. The will also work just fine on a manual exposure body. (AI-S = Auto-Indexing, Shutter.) The Nikon FA, FG, 2002 and 2020 use this feature; and that's it! All other bodies that can take an AI lens will use an AIS as if it's yet another AI lens. They are lighter than their AI predecessors, and there is some debate about whether they are better or not. In order to lighten them, material was removed and a portion of the lens converted to aluminum. Many claim the glass element and group formulations are the same.

Note:
You may also see "NAI" or "N/AI" lenses. These were made prior to the "AI" and the designation means "Non-AI." On some bodies, such as the F-2 with a Photomic metered prism, they could be semi-automatically indexed to the meter by rotating the aperture ring from one extreme to the other when mounting the lens.

There are are more nuances to the differences, but these are the main points and I don't believe I left anything important out.

-- John

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February 25, 2001