Automatic Exposure (AE) 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. (The three AC series lenses, extended from the FD lens mount, described below, are an exception). 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. Lens coatings, design variants The earliest breech-lock Canon FD lenses (1970-1973) are generally recognizable by a chrome (silver) 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 aperture ring could be rotated freely on and off of "o", although the small AE switch pin in the back of the lens (which came out when the aperture ring was rotated to "o") 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