Canon FD lens mount


The Canon FD lens mount is a physical standard for connecting a photographic lens to a 35mm single-lens reflex camera body. The standard was developed by Canon of Japan and was introduced in March 1971 with the Canon F-1 camera. It served as the Canon SLR interchangeable lens mounting system until the 1987 introduction of the Canon EOS series cameras, which use the newer EF lens mount. The FD mount lingered through the release of the 1990 Canon T60, the last camera introduced in the FD system, and the end of the Canon New F-1 product cycle in 1992.

Overview

The FD mount is mechanically compatible with and replaced Canon's earlier FL mount,which in turn had replaced the R mount; FD-mount cameras can use FL lenses in stop-down metering mode and R lenses will mount, but must be used with manual aperture and stop-down metering.
Though never officially explained by Canon, others have attempted to assign a meaning to the "FD" designation. One such attempt states that the "FD" notation stands for "Focal-plane shutter with Dual linkage for diaphragm control"; in actuality, there were two linkages and two signals: the automatic aperture lever, aperture signal lever, full aperture signal pin, and automatic exposure lock pin. This is twice the previous lens series, which used the "FL" designation, said to mean "Focal-plane shutter, Linked mount."
Over the 21-plus years of production, Canon introduced 134 different FD lenses ranging from 7.5mm through 1,200mm in seventeen different fixed focal lengths and nineteen different zoom ranges, one of the most, if not the most, extensive manual focus lens lines ever produced.
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. Indeed, sales of the Canon AE-1 camera alone exceeded one million.
Canon obsoleted the FD mount by its decision to create the all-electronic EF mount. Thus, the FD mount system, with limited provision for auto-focus, is now commercially obsolete, and Canon FD cameras and lenses are available for low prices on the second-hand market. This makes the system very attractive to 35mm film photographers who demand the highest optical quality, while not needing auto focus capability.
FD lenses can be used on many mirrorless interchangeable-lens cameras with a suitable adapter. They are a popular alternative to modern lenses among some users, though they lack autofocus.

Description

The FD lens mount is a breech-lock mount, which is a variation of the common triple-flanged bayonet attachment. The advantage of the breech-lock over the bayonet is that neither the contact surfaces between the body and lens, nor the signalling mechanisms, rotate against each other when the lens is mounted. This prevents any mechanical wear, which could conceivably reduce the very precise lens-to-film distance or introduce communication errors between lens and body.
The key pins and levers on the lens mount which transmit information mechanically between the lens and body include:
  • Automatic/Manual Aperture Lever – stops down aperture to the position selected on the aperture ring when the shutter is released; this can be moved all the way anti-clockwise to force the lens to operate in manual aperture mode only, such as when the lens is mounted on an early camera body with the R mount
  • Aperture Signal Lever – transmits the aperture selected on the lens to the in-body meter, which enables full-aperture viewing while providing accurate metering information
  • Full Aperture Signal Pin – transmits the maximum aperture of the lens mounted on the body
  • EE Switch Pin – signals the body when the lens is set for shutter-preferred autoexposure by moving the aperture ring to "A" or "o"
To mount the lens, the Positioning Pin is placed in the corresponding notch on the top bayonet lug and the breech-lock ring or lens body is rotated clockwise to lock the lens onto the body.

Versions

Canon's first generation of the FD breech-lock used the same rotating mounting ring at the rear of the lens as the earlier R- and FL-series lenses; the lens body itself did not rotate for mounting. There is a small pin which prevents movement of the breech-lock ring when the lens is not mounted on the camera. Its minor disadvantage was a somewhat slower lens change than a bayonet.
There are three different versions of breech ring FD lenses:
  1. The first version had a chrome plated front barrel and a green "o" for auto exposure.
  2. The second version had a black front barrel and still had a green "o" for auto exposure.
  3. The third version had a black front barrel, and a green "A" for auto exposure. These different versions are detailed below under variants.
Second-generation FD lenses, first marketed in 1979 as New FD, are mounted like bayonet-mount lenses in that the photographer twists the entire lens body to mount and dismount, though the actual mating surfaces still remain fixed. This retained the advantages of the breech-lock mount while enabling the convenience of a bayonet. The letters SC or SSC, to indicate the lens coating, were no longer put on the lenses. Canon documents stated that all new FD lenses except for the new FD 50mm F1.8 had SSC coatings. Canon later chose a bayonet-style mount for its EOS system's EF lenses, where there is no precision mechanical coupling.

Functions

Like its FL predecessor, the FD mount system allowed automatic diaphragm function, but in addition, a new signal pin supported full-aperture metering. A second signal pin for the "auto" setting of the aperture dial, plus a linkage to allow the camera to set the degree of diaphragm opening, enabled integral auto-exposure. The first camera to use this was the 1971 Canon F-1, when equipped with the Servo EE Finder. Later, the Canon EF of 1973 had automatic exposure built-in, as did the very popular Canon A-series cameras beginning in 1976.
Thus, starting with the first FD lenses produced in late 1970, all FD lenses had the capability of supporting full-aperture metering and multiple Automatic Exposure modes using both shutter-preferred and aperture-preferred modes. Even Programmed AE was possible with no modifications to the lens mount, though at the time of its introduction Canon did not have an AE camera body in the FD line. This was a design triumph for Canon that no other camera or lens maker was able to equal in 1970. Every other camera manufacturer had to make one or more alterations to its lens mount to enable full aperture metering, and later AE and or Programmed AE operation.
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.. While Canon could have adapted its mount to support auto-focus, as did other manufacturers, the company instead chose to make a clean break with the past and design a completely new interface with support for electrical signaling and control.

FD lens variants

Coatings and cosmetic changes

The earliest breech-lock Canon FD lenses are generally recognizable by a chrome filter ring at the front. Nicknamed 'chrome nose' lenses, these used two new proprietary lens coatings, designated "S.C." and "S.S.C.", but neither coating was signified on the front of the lens. These were both multi-coatings, but indicated two quality grades. In the 'chrome nose' series, only the large-aperture 55mm f/1.2, and 55mm F1.2 AL and the 7.5mm Fish-Eye lenses used S.S.C. coating. 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 aperture ring could be rotated freely on and off of "o", although the small AE switch pin in the back of the lens prevented one from doing this unless the body has the appropriate small hole in the proper location. There are chrome nose first generation FD lenses without chrome front barrels: several wide angle lenses and some telephoto lenses have black barrels, but their date code, lack of an aperture lock button and freely rotating breech ring place them into the first version FD lens group.
The second series of breech-lock FD lenses, which discontinued the chrome barrel front, is engraved "S.C." in white or "S.S.C." in red on the front of the lens. The S.S.C. coating was extended to most lenses in this series. The basic S.C. coating was, for the most part, limited to the least expensive lenses. These 2nd breech ring generation FD lenses still had a green "o", but now there was a chrome lock button on the aperture ring that had to be depressed to put the lens on or take the lens off of "o". One still could not put the lens on "o" unless the camera body had the AE switch pin hole. And the lens could not be mounted on a non-EE / AE body if the lens was set on "o". 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. Further, the breech ring rotated slightly when the lens was mounted to aid in getting the lens securely mounted. The aperture diaphragm was opened fully when the breech ring was in the locked position.
The third variant, made from 1976 to the end of production of breech ring FD lenses changed the green "o" to a green "A" and the chrome aperture ring lock button was changed from chrome to black. The breech ring was still locked unless mounted and it still had the spring loaded twist to make it easier to mount the lens. 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.
In 1978, with the introduction of the New FD series, the coating type was no longer specified on the lens front. All of these lenses received S.S.C. coating, with the sole exception of the 50mm lens. 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. When installing the lens, the entire body rotates except for the mating surfaces. This design allowed for the benefits of the precision breech lock and the ease of a bayonet mount. Image:CanonFDf1.8.jpg|thumb|Canon New FD 50 mm with caps.
The original breech-lock FD lenses and the New FD lenses are completely functionally interchangeable, and may each be used on any FD camera body. A minor operational difference between New FD and earlier lenses occurs only when using a Canon New F-1 body with the AE Finder FN in aperture preferred AE mode. The New FD lenses' aperture rings were placed closer to the rear of the lens so that the aperture value is visible in the new F-1's viewfinder, via an optical prism. Earlier lenses' aperture scales do not align properly with the prism, and are therefore not visible.