There are actually THREE different versions of the 55mm F1.2 AL / Aspherical lens. These correspond with the three different version of breech ring FD lenses. All three have the same optical formula. The first two versions had hand ground and polished aspherical elements. The third version had machine ground and polished aspherical elements.
The first version had the "chrome nose". The aperture ring had a green "o" for auto exposure (which was only possible at the time this lens was made if one had an F-1 with the Servo EE Finder), and there was no locking of the aperture ring when set on "o". The breech ring could be turned freely, there was no locking detent on the ring. This 55mm had blue AL letters on the barrel front and a gold line around the front of the barrel. It had SSC coating but it is not marked. These were made up to around early 1973.
The second version, made from 1973 to around 1976 or so, had black nose (complaints about flare, etc led both Canon & nikon and well as others to make the front of the barrels black). This version has SC or SSC as appropriate for the lens coating. The aperture ring still had a green "o" but there was a chrome button that one had to push to put on the lens on or to take the lens off of "o". The breech ring now had a locking detent to prevent the ring from turning unless one put a cap on or put the lens onto a body. The breech ring was also spring loaded to turn slightly to aid in getting the lens mounted. The 55mm Aspherical still the blue AL and the gold line, but also added the SSC letters on the barrel.
The third version changed the green "o" to an "A" and the chrome aperture ring auto lock release went from chrome to black. This change was probably made to match up with the nomenclature in the new A-series bodies. This third version also used plastic front barrels in a few of the lenses, most notably the FD 50mm F1.8 SC. The 55mm Aspherical lens no longer had the blue AL or the gold line but the word "ASPHERICAL" in gold lettering before the red SSC letters.
