For the canon eos 1dmkiimkiin and 1dsmkii digital slr cameras the anti fog eyecup ec is useful in cold weather to prevent users breath from condensing on the eyepiece lens its also handy in hot humid weather to prevent fogging from evaporation around the users eyes or when stepping from a cool environment into a hot one please note this eyecup will not fit the canon eos 1d mkiii or 1ds mkiii cameras