The C-3 brick could take three lenses. A 35mm, the normal 50mm Cintar, and a 100mm Tele Sandmar. Enna Werke also made lenses for Argus cameras. They weren't hard to change, just unscrew the knurled nut on the rangefinder coupling gear, remove the gear, unscrew one and screw on another. The most well known interchangeable lens model was the C-44. It had much the same focal lengths available. It was also known for being the most stubborn, hard to change setup ever made. I have one of those too. Other interchangeable lens setups were, if memory serves, the C-33 and the Geiss modified C-4.