This Hoyarex 21 UV filter is 75mm square for the Hoyarex filter system. It comes in a hard plastic protective case and, unlike most other Hoyarex filters, has a plastic frame so you can hold the filter without touching the actual optical area. This is a glass filter so optically superb and hard to find. Leave it in the holder when shooting water or in rain to prevent splashes on the front element. The Hoyarex UV filter is used to reduce haze when shooting in daylight and can imporve clarity of your photos. Works with film or digital cameras.