The Opteka FD (Manual Focus) System to Canon EOS (Auto Focus) Series Cameras Lens Adapter allows the use of older Canon FD series lenses on Canon"s EOS (auto focus) series cameras.Unlike other simple mount adapters, this is an optical adapter which is actually at the same time also a short teleconverter, which increases the focal length by a factor of 1.25x, and reduces the lens aperture by approx. one f/stop. This adapter allows for focusing at infinity.