Production 1968-1971 Backs were removeable for 250 exposure back. Polaroid back could be used if camera modified This special release was tagged with Apollo due to this camera being used by NASA. Nikon with prong on lens for wide-open metering. All other Nikon mount will work with different metering. FTN metered head installed provides TTL metering. ISO 6-6400, Measures approximately 6.5 x 5.4 x 2.6 in.