the C 3 "brick" took a 35mm lens and a 100 mm lens as well as the standard 50. To remove it you unscrew the cap on top of the gear between the lens and the focusing knob, remove the gear and unscrew the lens. New lens screwed in, put the gear back (resetting the lens to infinity on the rangefinder scale is by trial and error" and put the cap back on.

not exactly a quick system to use.