what is AI lens? and what is Stop-down mode? Thank you.

-- ik (ik_np@yahoo.com), February 19, 2002

Answers

Older Nikon lenses had a little prong on top that engaged a pin on the Nikon F Photomic finder, or on the Nikkormat. That's how the lens told the camera what f-stop you had set it to. The process of the lens telling the camera this information is called indexing. The meter needs to know this to get the exposure right.

On nwer lenses, they built the indexing right into the back of the lens. That way, you don't have to fuss around and waste precious time getting the little pin lined up with the little doodad on the lens. This newer way is called Auto-Indexing, or AI for short.

Non AI lenses won't work in automatic mode on a present-day Nikon. But you can use them anyhow, by manually stopping down to the selected aperture using the Depth-Of-Field Preview lever, as you take the exposure reading. That's called stop-down metering.

Most non-AI lenses can be converted to AI for a charge. Sometimes it's worth it, sometimes not.

-- Bob Fleischman (RFXMAIL@prodigy.net), February 19, 2002.