Canon FD lens mount

This is twice the previous lens series, which used the "FL" designation, said to mean "Focal-plane shutter, Linked mount.

[citation needed] The Canon FD system enjoyed huge popularity in the 1970s and 1980s, when it established and grew a market share with professional photographers as well as having equipped over a million consumer users.

This makes the system very attractive to 35mm film photographers who demand the highest optical quality,[4][5] while not needing auto focus capability.

This prevents any mechanical wear, which could conceivably reduce the very precise lens-to-film distance or introduce communication errors between lens and body.

Canon later chose a bayonet-style mount for its EOS system's EF lenses, where there is no precision mechanical coupling.

Like its FL predecessor, the FD mount system allowed automatic diaphragm function, but in addition, a new signal pin supported full-aperture metering.

The FD mount has no support for either electrical or mechanical lens-body communication required for autofocus, which was a primary reason for its retirement.

This first series of FD lenses shared other characteristics that would later change; the breech-lock ring can be rotated freely without mounting it on a camera body, and the aperture ring had a green "o" at the end of the scale to indicate automatic aperture operation, which at the time was only possible with an F-1 body that had the Servo EE Finder attached.

The second series of breech-lock FD lenses (1973-1976), which discontinued the chrome barrel front, is engraved "S.C." in white or "S.S.C."

The breech ring now featured a lock which prevented it from rotating unless a rear cap was put on or the lens was mounted to a body.

The third version FD 50mm F1.8 lens also received a plastic front barrel to reduce size and weight.

This corresponded with the introduction of the Canon A-series cameras which were smaller and lighter than the older, larger and heavier "F-series" bodies.

New FD lenses are easily identifiable by the replacement of the breech ring with a square metal release button at the base of the lens.

In addition to more robust mechanical construction, these lenses used a variety of special technologies, including ground aspherical surfaces, fluorite optical elements, and ultra-low-dispersion glass.

Ultra-low dispersion and fluorite elements virtually eliminated chromatic aberration at long focal lengths.

[7] The earlier versions of these lenses carried "AL", "Aspherical", or "Fluorite" indications on the front of the lens.

The post-1979 'New FD' versions acknowledged all the exotic technologies under the single designation "L" (commonly believed to indicate 'luxury' or 'asphericaL').

Canon has continued the "L" designation, and the famous red ring around the lens front, in the current EF and RF autofocus lenses for EOS cameras, where the symbol now officially stands for "Luxury."

The FD series included a number of zoom lenses with close-focusing mechanisms, targeted at amateur photographers.

Though it uses the breech-lock mount, it is not literally an FD lens since its diaphragm is operated manually and it must be used with stop-down metering.

The photographer may introduce three levels of spherical aberration by sliding the focusing ring forward or backward.

The autofocus system was activated by a button on the side of the lens, and involved no communication with the camera body.

FD lenses can be adapted to other cameras with longer flange focal distances, though the lenses cannot focus to infinity unless the adapter contains an optical correction element which may compromise image quality, as it is not part of the original FD lens optical design.

The adapter was produced in limited numbers, with the intent of easing the initial cost of conversion for professional users who owned expensive FD telephoto lenses.

Other inexpensive aftermarket FD to EOS adapters are available and can be used at the cost of severely reduced image quality, particularly at large apertures.

It has a flange focal distance of only 20mm and a 2× crop factor, halving the field of view compared to the original 24x36mm film frame.

As of 2012, with the introduction of the Canon EOS M mirrorless camera, almost all FD or FL lenses can be successfully adapted with infinity focus available without the need for a compensating lens, thus not compromising resolution, contrast and distortion performance.

[12] FD lenses can also be mounted to current mirrorless digital cameras with short flange focal distance, using simple mechanical adapters without optical correction.

FD lenses, especially wide and ultra-wide f/2.8, f/2 and f/1.4 variants, have proven popular options for videography for these mirrorless formats.