Emily Non AI Nikkors used the Meter Coupling Prong to engage a small lever in the optional meter prisms (the standard prisms were called eye level and had no metering capabilities) of the F and F2. That was how the meters gave you wide open apertures for focusing. You had to rock to the aperture ring back and forth to both maximums to let the meter know what the max aperture was on the lens being used. AI (Auto Indexing) Nikkors kept the Meter Coupling Prong only to ensure backward compatibility with older Nikon bodies. A ridge was added to the mount of the lens that acted the same as the Meter Coupling Prong to provide again, the wide ap for focusing and communicated to the camera the max ap. AIS (Auto Indexing with a "shutter" designation) lenses upto the AF series, again kept the Meter Coupling Prong, and the ridge and added a small notch added to the mount which communicated with the camera, additional information about the lens being used such as focal length and maximum ap and if I'm not mistaken allowed Shutter Priority modes. Series E lenses were built as a consumer line for the long discontinued Nikon EM, a consumer version of the Nikon line. They had lots of plastic but the optics were traditional Nikkor. ED is the designation used by Nikon to designate the extra low dispersion qualities with some of their lenses. An ED lens has additional coatings on some of the internal elements or groups. Non ED lenses have the standard coatings. Similar to the "L" desgination of the canons. AF lenses use the AIS mounts. You can add any lens to any camera almost. NO other camera manufacturer can make that claim. Non AI lenses should be used cautiously on the newer Nikon bodies. But, I can use an Ai on an F5 and still get metering capabilities. I can not obviously get shutter priority, and the aperture setting does not show up in the VF or on the LCD readout. I set my ap and "know" what I have it set to or look at the aperture ring when I need to change my aperture. Take care, Gregory david Stempel FIREFRAMEi m a g i n g www.americanphotojournalist.com "The brave ones were shooting the enemy, the crazy ones got it on digital"
