FD Lenses
From Wikipedia, the free encyclopedia
The Canon FD lens mount is a physical standard for connecting a photographic lens to a single-lens reflex camera body. The standard was developed by Canon of Japan and was introduced in March 1971 with the Canon F-1. It was the primary Canon SLR lens mounting system until 1987 when the cameras from the Canon EOS series were first produced. The last camera in the FD system was the Canon T60, from 1990. The FD mount replaced Canon's earlier FL mount; FD-mount cameras could use FL lenses in stop-down metering mode.
There is no definitive meaning agreed upon for 'FD', and Canon has never said what it stands for.
While the capabilities of FD-system camera bodies increased dramatically, the capabilities of the lens mount remained unchanged, apart from the unique autofocus system electrical contacts used by the T80 and its AC lenses. However, lenses in the FD mount evolved over the years. Initially, all the lenses had silvered metal locking rings at the base and only that ring turned to lock the lens to the mount. In 1976 the New FD lenses were introduced. In these, the whole lens barrel rotated to perform the locking action, and the lens barrel was all black; Canon's Super Spectra Coating was now standard on all lenses except for the 50 mm f/1.8, and the lens markings no longer specified it. In the very late 1970s, Canon introduced its L (Luxury) lenses—a new range of expensive lenses of high optical quality.
The massive popularity of this system combined with its current obsolescence makes it readily available for reasonable prices on the used market.
In 1973, two years after the FD mount was introduced Canon started using the Super Spectra Coating (SSC) on its lenses and marked them with "SSC" on the lens.
In 1976, the "New FD" mount was introduced and SSC became standard and the marking was removed.
The FD lens mount is a breech-lock mount. The advantage of this type of mount is that the contact surfaces between the body and lens do not rotate against each other when the lens is mounted. This prevents any abrasion, which could conceivably reduce the very precise lens-to-film distance. The disadvantages include slower lens changes; later FD lenses mounted more like bayonet-mount lenses in that the photographer twisted the lens body to mount and unmount, even though the actual mount surfaces stayed fixed. Canon chose a bayonet-style mount for its new EOS system's EF lenses.
The major new feature of the FD mount was support for auto-exposure metering. This allows the camera body to determine the aperture setting and tell the lens what value to use. The camera body already controls the shutter speed, so this allows for completely automatic exposure control.
The FD mount has no support for the lens-body communication, whether electrical or mechanical, required for autofocus, which was a primary reason for its retirement; Canon could have adapted its mount to support auto-focus, as did other manufacturers, but instead the company chose a clean break with the past and an electrical only interface.
Canon did however manufacture a single lens containing a lens-integral autofocus system — the FD 35-70 mm f/4 AF. The autofocus was triggered by a button on the side of the lens, and involved no communication with the body. It was reasonably accurate with still subjects, but was too slow to be a practical solution for moving subjects such as sports.
The flange focal distance of the FD mount is smaller than most other lens mounts, meaning that it is impossible to mount a FD lens with an adaptor onto most other cameras and maintain the same distance. Canon made an adaptor containing corrective optics allowing its larger, more expensive FD telephoto lenses to be used on EOS bodies. This adaptor functioned as a mild tele-converter, and could not be used on normal and wide-angle lenses. Canon produced this adaptor to ease the initial cost of conversion for those with expensive collections of long FD telephoto lenses.