The F2S Photomic (DP-2 head) and F2SB Photomic (DP-3 head) also accepted the unusual Nikon DS-1 or DS-2 EE Aperture Control Units. The F2AS (DP-12) required the equivalent DS-12. These were early attempts by Nippon Kogaku to provide shutter priority autoexposure by having an electric servomotor automatically turn the lens aperture ring in response to the set shutter speed and light meter reading. The DS-1, -2 and -12 were bulky, slow and unreliable, and were feeble and inelegant attempts to add autoexposure to the manual exposure F2.