Camera Lens Parts: Rear Group Protection Ring
The rear group protection ring refers to the ring at the back of a camera lens where the rear lens cap screws onto. It is very important to keep the rear group protected at all times because it houses the lens, the aperture and the electrical connector strip. If one of these were to be damaged, it would cause the lens to either need to be repaired or even replaced.
How It Works
Unlike the front lens cap, the rear lens cap screws onto the lens rather than popping on. This helps keep this lens cap securely attached so that the risks of dents and scratches are greatly reduced. These rear lens caps come with the lens when it's purchased and are usually made out of plastic. Some larger and more expensive lenses use metal screw on caps rather than plastic ones.
Keeping It Clean
It's always a good habit to keep a can of compressed air in your photography kit. If dust or other foreign objects are able to make their way into the rear lens cap or inside the lens, it can ultimately travel back into the camera where it could threaten the image sensor. A damaged sensor can be very expensive to replace. This damage can be prevented by taking proper care of the rear lens area and lens cap.