The BlackRapid LensBling is a rear lens cap. What makes this rear lens cap special is the focal length of the lens is labeled in clear, bold numbers on the outside of the cap. When your lenses are in your camera bag it"s not always easy to tell which lens is which. Having the focal lengths clearly printed on the rear lens cap will save you that brief moment of doubt as you reach to change lenses and could be the difference between getting your shot and not.