Exacta introduced the 1st practical SLR and there were offerings from Contax such as the Contaflex and Contarex. Also, Alpa but, not a major market player. In the '50s with the introduction of the 1st slr with the now common mechanical layout, the Contax and then the Ashahiflex (think it was called that), the slr market was established. When Ashahi added the internal metering (Spotmatic), the die was cast against all other designs that made up the majority of the market. I remember attending a photo show as a kid after the slr offerings took hold and a marketing manager from Asahi said every camera maker had to either go slr or go broke. It was like the transition from tubes to solid state, persons could not get rid of obsolete Rolleiflexes, Leicas, Nikon and other rangefinders and cameras like the Speed Graphic and other mf and lf cameras used by news agencies, etc. were relegated to the scrap heap as suddenly the 35mm was legit where for deacades before, none would consider it good enough to use even for a newspaper photo. A great time to collect some great vintage cameras for next to nothing.