In fact Leica had problems in making a fast 50mm in the early years. In the 1930's they had the Xenon 50mm f/1.5 for the Leica, but that lens was designed and made by Taylor, Taylor and Hobson in England. However, the Zeiss Sonnar 50mm f/1.5 for the Contax was a much better lens. After the war they had the Summarit 50mm f/1.5, but that was only a coated version of the Xenon, also made by TTH. The first Summilux 50mm f/1.4 in 1959 was an extremely good lens, but that lens too was made under patents by TTH, so Leitz had to pay TTH for every Summilux 50mm f/1.4 v1 they sold. Finally they came up with their own design, the Summilux 50mm 1.4 v2 (from serial nr. 1844001). It was a weak lens with lots of distortion and a problematic rear group due to tensions in the sealant surfaces. So they had to come up with something NEW. That was the Noctilux 50mm f/1.2, in 1966.
Erik.