Canon SLR (single lens reflex) cameras have two types of lens mounts: EF and EF-S. EF-S lenses are designed to fit smaller SLR cameras with smaller digital sensors and feature a protruding back element that makes the lens fit only EF-S mounts. While an EF-S mount can hold both EF and EF-S lenses, EF mounts can hold only EF lenses. However, you can convert EF-S lenses to fit into an EF mount. Only do this with small frame Canon SLRs such as the 10D and 20D, as full-frame cameras like the 1D have a larger mirror that will collide with EF-S lenses if they are mounted on the cameras.
Instructions
1. Remove the four screws that hold the lens mount. These screws are on the back of the lens--the part that attaches to the camera--and are the only screws at the center of the mount. The screws are affixed with a light glue, so it may take a bit of pressure to remove them.
2. Remove the mount by carefully sliding the screwdriver between the mount and the rest of the lens and slowly prying the mount off. Although the four screws primarily held the mount, there is also a light glue that adheres the mount to the lens.
3. Unscrew the single, raised screw near the electrical contacts at the back of the lens.
4. Lift the rest of the lens mount slightly until you can see four plastic clips that hold the mount in place. Carefully insert your screwdriver between the lens mount and the lens itself and manipulate the clips until they release the mount. This mount makes the lens physically unable to fit into an EF lens mount, and when it is removed, the lens will fit into an EF mount like a standard EF lens.
Tags: EF-S lenses, lens mount, four screws, into mount, light glue, makes lens, mount lens