The first Leica prototypes were built by Oskar Barnack at Ernst Leitz Optische Werke, Wetzlar, in 1913. Intended as a compact camera for landscape photography, particularly during mountain trips, the Leica was the first practical 35 mm camera, using standard cinema 35 mm film. The Leica transports the film horizontally, extending the frame size to 24×36 mm, instead of the 18×24 mm used by cinema cameras which transported the film vertically, with a 2:3 aspect ratio. The Leica went through several iterations, and in 1923 Barnack convinced his boss, Ernst Leitz II, to make a prototype series of 31. The camera was an immediate success when introduced at the 1925 Leipzig Spring Fair as the Leica I (for Leitz camera). The Elmar 50 mm f/3.5 lens (a 4-element design influenced by the Zeiss Tessar) was designed by Dr. Max Berek at Leitz. The focal plane shutter had a range from 1/20 to 1/500 second, in addition to a Z for Zeit (time) position. In 1930 came the Leica I Schraubgewinde with an e