He wanted the quality and the portability. Ten years later, he managed to put theory into practice. He made the first prototype of 35mm camera and named it: Ur-Leica.
The film 24mm x36mm was created by doubling the cinema film format. After several tests and research Oscar Barnack found that the new format, had the quality to hold photographic data for a long time, and the quality was also comparable to the glass plate film.
The first camera that was introduced by Leica was a rangefinder camera. It's small and compact, you can slip it easily into your pocket. The built quality was also superb. Right after the first Lecia was launched, the World War I broke and the rangefinder was used by military to document the war. It was the first debut of a small, compact, and portable 35mm camera.
Later on, in Japan, an optical company called Nippon Koggaku, k.k or Japan Optical Co. Invited some of the Lecia's finest techinicians to come over to Japan and share the knowledge about lenses industry. The invitation was sent out in 1919 and the technicians arrived in 1921. With the help from German technicians, Nippon Koggaku managed to raise their standard to the level of Lecia as one of the leading Optical industry. But the idea of small compact 35mm cameras still didn't impress the Japanese. However, Nippon Koggaku (changed their name to "Nikon") produced lenses for glass plate cameras. Also, they produced lenses for a small optical company called Hansa Canon (without knowing that Hansa Canon (Canon) became their main competitor in the camera industry few years later.).
The production of 35mm cameras didn't start until post-WW II. During the war, Japanese used Leica rangefinders to record the war. The rangefinders were luxury item because they were imported from German. After losing the war, the economy was totally bad, but Nikon managed to re-structure the company, started all over again with couple hundreds employees.