Back in the day, 1950's or so, there were a lot of work arounds for rangefinder cameras because so many were sold and 35mm SLR's had not quite 'arrived' yet. Sure, there were Exakta's and Pentax had a M42 mount camera out by 1957 and Praktica had a reflex in the 50's also. But the SLR solved so many of these problems in their design. That said, the big jump in 35 SLR sales started in the 60's and by the 70's there were so many quality cameras available, all the major Japanese camera companies were well represented. In the 70's I was a salesman at Altman's in Chicago and we pushed so many SLR's across the counter is was amazing. On an average day 10 or 15 Minolta SRT's were sold, not to mention numerous Pentax, Nikon, Canon, Olympus, Topcon (remember those?), Konica, so many I cannot remember them all. The smaller store front camera stores around the Loop would buy 6~8 cameras at a time from the reps. Ralph Altman bought popular SLR's like the SRT in pallet load quantities. Seems like everyone and their dog had to have a SLR.