Canon EX lenses are not truly interchangeable. They were made to fit only the Canon EX EE and EX Auto models. To save money, the rear half of the lens, including the aperture diaphragm, remains permanently attached to the front of the camera. The front half of the lens unscrews and is interchangeable.
- Canon 35mm f/3.5 EX
- Canon 50mm f/1.8 EX
Jonathan Gazeley 
Full list also includes 95 and 125, both f/3.5, total of 4 front ends to these 2 cameras. Neat package if you ask me and the cameras are outstanding.
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