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 full auto-exposure. When the lens was set to auto exposure (AE) the camera chose the aperture and this was communicated to the lens by this second signal pin. When the shutter button was pressed the original aperture pin was engaged by the camera to stop the lens down to the setting chosen by the camera and communicated to the lens by the second signal pin.

The first camera to utilize 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, the AT-1 being the one exception. The earliest breech-lock Canon FD lenses (1971-1973) are generally recognizable by a silver chrome filter ring at the front (this ring includes its own bayonet used to mount an appropriate lens hood). Nicknamed ‘chrome nose’ lenses, these used two new proprietary lens coatings, designated “S.C.” (Spectra Coating) and “S.S.C.” (Super Spectra Coating), 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 (Aspherical) 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 second series of breech-lock FD lenses (1973-1979), which discontinued the chrome filter rings, 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. Changes were made across production, resulting in two minor variants of this second series. The earlier variant retained the aperture ring and breech-lock ring details of the earlier lenses. The later variant used a green letter “A” to indicate that the lens was set for AE operation, and the aperture ring had a small lock button to prevent the lens from being accidentally taken on off the “A” setting. The later variant also featured a latch to hold the breech-lock ring in the mounting position until pressed to the camera, at which time a spring caused the ring to rotate a few degrees, making it somewhat easier to mount the lens.

In 1978, with the introduction of the New FD series (nicknamed ‘FDn’), 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 f/1.8 lens. These lenses are mounted like bayonet-mount lenses in that the photographer twists the entire lens body to mount and dismount the lens, though the actual mating surfaces still remain fixed. There is a square silver metal button at the base of the lens that unlocks the lens when you decide to remove it from the camera. This new arrangement retained the advantages of the breech-lock mount while enabling the convenience of a bayonet.

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, it did not. 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. 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.

FD Lenses in the Collection

FD 50mm F/1.8 S.C. (II)

FDn Lenses in the Collection

No, these are not lenses in my collection (I wish!). This is from a Canon advertisement. Impressive!