Of the 23 lenses Max Berek engineered for Leica, the Summar 50 mm f/2 was the first to offer high light sensitivities at a normal focal length. Consisting of six elements in four groups, the lens was an improved version of the Double Gauss design, invented in the early 19th century by German mathematician Carl Friedrich Gauss.
Originally developed for astronomical telescopes, the design is based on one convex and one concave lens to minimise optical aberrations. Leica manufactured the Summar 50 mm f/2 from 1935 to 1940. Its combination of speed and focal length have defined our understanding of the term "standard lens" to this day.