Canon's 50mm f/1.2 in Leica screwmount (39mm x 26 tpi) is something of a legend. Introduced in 1957/58, it is very fast and today it is relatively affordable. The main alternatives, after all, are either Leica Noctiluxes (the 50mm f/1.2, 1966, discontinued, or the 50mm f/1, 1967, still current) or...