The AE-1 has a Canon FD breech-lock lens mount and accepts any FD or New FD (FDn) lens. It is not compatible with Canon's later Canon EF lens mount, though adapters made by independent manufacturers can be found. The camera will also accept Canon's earlier FL-mount lenses through the use of stop-down metering. Original FD lenses, introduced in 1971, do not rotate in the mounting process; instead, a locking ring at the base is turned to attach the lens. This was often criticized as being slower than the bayonet mounts of competing cameras. The counter argument, though, was that as the lens/body mating surfaces did not rotate, there was no wear that could affect the critical distance from lens to film plane. In 1979, Canon introduced the New FD series of lenses that rotate the whole "outer" lens barrel to lock. The inner lens barrel remains stationary, and thus the signal levers and pins still do not rotate. During the late 1970s, there were over 50 Canon FD lenses available for purchase. They ranged from a Fisheye FD 15 mm f/2.8 SSC to a FD 800 mm f/5.6 SSC, plus special purpose lenses such as a 7.5mm circular fisheye and a 35 mm tilt and shift lens.