An online guide to collectable cameras and related stuff
Canon Rangefinder Identification Guide
Canon 7 Series
Why was it so sucessfull? Lack of competition. The M3 was more expensive. Nikon had dropped their rangefinder line in favor of the SLR Nikon F. Zeiss had discontinued the Contax line in 1961. Yashica had assorbed Nicca (who had also produced legions of Tower cameras for Sears) and then moved into fixed lens/leaf shutter rangefinders and TLR cameras.
The Canon is easy to identify. It says Canon 7 on top. Some are marked "Bell and Howell/Canon 7"
The last model of Canon rangefinder is actually two models. They are both marked Canon 7s on top. The first model is the Canon 7s. It can be identified by the rangefinder adjustment port, a small chrome plug with two little holes for a spanner wrench, located right next to the shutter speed dial. They built this camera from 1965 until 1967, producing about 16,000 cameras.
In 1967 they redesigned the finder on the 7s. The easy way to identify it is that the rangefinder adjustment port is above the second "n" in Canon on the top of the camera. But the rangefinder era was drawing to a close. They had only produced about 4000 of these when Canon abandon the system rangefinder in sept 1968.