Summicron

The name Summicron is used by Leica to designate camera lenses that have a maximum aperture of f/2 after 1953 and to present day.

In the 1950s Leica bought Crown glass from Chance Brothers, an English company and used it to make the lenses.

[1] Leica designed a number of f/2 lenses before the Summicron, such as the Summar and Summitar.

New coating technologies available after World War II allowed for the creation of the Summicron lens.

[1] Faster Leica lenses are offered with the trade names Noctilux (or Nocticron) and Summilux.

Leica Summicron-R 50 mm f/2 II 'Safari' edition from 1978.
Leica APO Summicron-M 50 mm f/2.
Leica Summicron-M 50 mm f/2 from 1960.