Dirt and debris can prevent a lens ring from turning.
The Canon EFS 18-200mm is a compact zoom lens that will cover most focal lengths you would encounter in day to day shooting. The lens features Canon's Image Stabilization system designed to help create crisp pictures by minimizing camera shake. The lens is not one of Canon's L series lenses that features a higher degree of sealing that prevents dirt from collecting inside. The lens has two rotating rings in its design, one for focusing, and one for the zoom function. Should either of the rings become stuck, you can do a few things to try and free them.
Instructions
1. Inspect the lens. Remove the lens from the camera, and under a desk lamp or other light source, inspect the lens to see if you can identify any foreign object that may be preventing the ring from turning.
2. Remove the four small screws on the metal mounting ring at the rear of the camera.
3. Remove the ring from the camera, being careful not to pull or stretch the ribbon cable that is connected to the lens contacts.
4. Inspect the inside of the lens compartment for any debris that may be in the guide rail or motor grooves. If something is visible, do not use compressed air to remove the object as it may cause the debris to go farther into the lens.
5. Use a small pair of tweezers to pick up the debris, or place a small amount of two-sided tape to the end of a pencil and try to pick up the debris.
6. With the debris removed, confirm that the ring is free to rotate. Re-assemble the lens.
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