The F2A Photomic came with the DP-11 head; the F2AS Photomic used the DP-12 head. The DP-11 and DP-12 (both introduced in 1977) functioned exactly the same as the DP-1 and DP-3, respectively, except that these heads supported Nikkor lenses with the Automatic Indexing (AI) feature (introduced 1977, see above). Nikkor AI lenses had a "meter coupling ridge" cam on the lens aperture ring that pushed on a spring-loaded "meter coupling lever" on the Photomic head to transfer aperture setting information. AI lenses allowed carefree lens mounting and ended the double twisting that used to allow observers to spot a Nikon/Nikkormat user from a hundred paces. The F2AS Photomic (DP-12 head) was the most advanced F2 version and the chrome version with Nikkor AI 50 mm f/1.4 lens had a US list price of $1,278 in 1978. (SLR selling prices were typically 30 to 40 percent below list.) This, the last version of the Nikon F2 Photomic, has become the most desired and collected F2 today.