The Leica had several model iterations, and in 1923, Barnack convinced his boss, Ernst Leitz II, to make a preproduction series of 31 cameras for the factory and outside photographers to test. Though the prototypes received mixed reception, Ernst Leitz decided in 1924 to produce the camera. It was an immediate success when introduced at the 1925 Leipzig Spring Fair as the Leica I (for "Leitz camera"). The focal plane shutter has a range from 1/20 to 1/500 second, in addition to a "Z" for "Zeit" (time) position.