Canon Lens format abbreviation - this is the old manual focus Canon lens mount used before 1987. Because it was not suitable for autofocus, Canon decided to switch from FD and designed the EOS system with EF mount. Canon FD is now discontinued, but still used by film photography enthusiasts. There are some cracking lenses with the FD mount and, through the use of appropriate adapters, FD lenses can be mounted on modern EOS EF cameras. Adapters with an optical glass element allow infinity focus, while simpler adapters without an additional optical element will not focus at infinity.