The Hitech 85mm UV 2B Absorbing Resin Filter reduces the bluish cast of daylight and produces a pleasing, warmer picture tone. It helps protect your lens from dust, moisture and scratches, which can lead to costly repairs. If desired they can be left on at all times for protection. Skylight filters provide additional benefits of correction for Ultraviolet (UV) light which can register on film and videotape as a bluish cast and can obscure distant details. Also used to reduce the bluish cast common with some electronic flash units. This is an 85mm square skylight (2B) filter made from CR39 optical resin and is specific to the Cokin P-series filter holder.