The top-class 35mm camera market gradually shifted from rangefinder cameras to single-lens reflex cameras. The major reason was that SLRs could handle close-ups, photomicrography, duplication work, and other applications without being constrained by the limits of rangefinder camera lenses. When Canon introduced the Canonflex, its first SLR, there were already eight SLR models on the market.

The Canonflex used a high-quality, breechlock lens mount. The lens flange ring was turned to lock the lens onto the camera flange’s bayonet lugs. The lens flange and camera flange did not rub against each other like today’s lens mounts. The camera used Super-Canomatic lenses which had a fast, fully-automatic diaphragm. A 130-degree winding trigger at the camera bottom enabled quick film advance. An external selenium exposure meter could also be attached.