> I have been in the market for a used 24 mm and came across one today. I > read the archives as well as Moose Peterson's Nikon System Handbook. I > have these questions: > 1. what is AI? (I know it means auto indexing, but what is that?) See question 2. > 2. the man behind the counter said this lens had been "AI-d". A section > was cut away which, apparently, makes it "AI-d". If he was correct, > what does this mean? Pre-AI lenses transmit the aperture to the camera via the prong on the aperture ring. AI lenses transmit the aperture via the cam (cut away section) on the aperture ring. There are other slight differences which have no effect on the N90. > 3. What do I lose/gain with this lens vs. a new AFD? You loose AF! You loose distance metering and matrix metering You keep weight centered and spot metering You loose shutter priority and program modes You retain manual and aperture priority Both have DOF scales The manual lens has a longer focus throw so focusing is slower and more accurate, the DOF scale is wider to match the wider focusing scale. You gain silky smooth focusing ring and rugged all-metal construction Both lenses have CRC, the early manual lens has an older optical design - reported to be very good Hope this helps, Roland
