Ihagee's Kine Exakta is widely considered the first popular 35mm SLR ever made. This camera, as well as its followups, all use the Exakta mount. This system, introduced in 1936, opened the door for 35mm SLR photography. SLRs allowed for far more photographic applications than rangefinders, including medical photography, microscopes, telephoto lenses, etc.
Over 20 Exakta camera models were produced from 1936 to 1969. The Exakta mount was used with minor modification by Tokyo Kogaku in their Topcon cameras, so there is lens interchangeability between the two systems.
Lenses for Exakta systems were made by many manufacturers like Carl Zeiss, Meyer Optik, Schneider-Kreuznach, E. Ludwig, Enna, Kilfitt, Isco-Göttingen, Rodenstock, Schacht & Steinheil. One of the best known lenses for the Exakta system is the Carl Zeiss 58mm F2 Biotar lens. The Biotar design was later used by many Russian and Japanese lens manufacturers.