Barnack's words, "Small negatives -- large images", would soon change the world of photography.
The concept was developed further, 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 in Leipzig as the Leica I (for Leitz Camera) in 1925. The Elmar 50 mm f/3.5 objective (a 4-elements design influenced by the Zeiss Tessar) to was designed by Dr. Max Berek at Leitz, and was one of the reasons behind the success of the camera, the other being its compact size and reliability. 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 exchangeable objective system based on a 39.5 mm thread. In addition to the 50 normal lens, a 35 wide angle and a 135 mm telephoto objective were initially available.
The Leica II came in 1932, with a built in rangefinder coupled to the lens focussing mechanism. This model had a separate viewfinder (showing a reduced image) and rangefiner (showing an enlarged double image which was properly focussed when it became one image). Leitz (and Barnack) continued to refine the original design through to 1957, the final version being the IIIG, with a the shutter ranging from 1 second to 1/1000 second. These models all had a functional combination of circular dials and square windows that was quite esthetically pleasing, although quite busy in appearance.
In 1954 Leitz unveiled the M3, a bayonet lens model, considered by many to be a design miracle for its combination of simple appearance with functional flexibility. It combined the rangefinder and viewfinder into one extremely bright window with an even brighter double image in the center, providing so much light that one could almost focus in the dark! In addition, it had a new rubberized focal-plane shutter, which is known for reliability and is probably the quietest focal-plane shutter ever made. This model has continued to be refined (the latest versions being the M7 and MP, both of which have frames for 28, 35, 50, 75, 90, and 135 mm lenses which show automatically upon inserting the different lenses); but the basic quality and simplicity of design has not changed.
Leitz was also responsible for numerous optical innovations (first use of aspherical production lenses, first use of multicoated lenses, first use of rare earth lenses, to name a few), and Leica lenses developed a mythology about them -- that photographs taken with them were recognizable from photographs taken with other lenses. There has been much controversy about that.
Due to the strength of the Leica brand, the Leitz company changed its name to Leica in 1986. The Leica company still produces a range of expensive but very high quality optical products, including compact cameras, M-System rangefinder cameras (as direct descendants of the first Leica), R-system single-lens reflex cameras, digital cameras (in association with Panasonic), binoculars, and spotting scopes.