With this Olympus POSR-EP09 UW Anti-Reflecting Ring, you can ensure that unwanted writing on the front of your M.Zuiko Digital 25mm f/1.8 lens does not show up in your underwater photos or videos. The ring fits onto the front of the lens, and blocks the aperture, focal length, and other writing from being reflected in the front element of a compatible lens port on an underwater camera housing. Its 46mm diameter matches the filter thread size of the 25mm f/1.8.