in may 1959, the canonflex slr was introduced. the camera featured a quick return mirror, an automatic diaphragm and was introduced with an interchangeable black pentaprism housing. it also featured newly developed 'r' series breech lock mount lenses. this slr was superseded by the canonflex rm, a fixed prism slr which featured a built-in selenium cell meter. later came the canonflex r2000, with a top shutter speed of 1/2000 of a second. this model was also superseded by the canonflex rm.