Pure Harmonie Anti-UV filters are the thinnest and the lightest in the world. With a thickness of 3.3mm they are almost invisible when mounted on your lens. Their weight is so light that you won"t even notice that they are attached. They have been engineered with no compromise: very robust, compatible with all lens caps, and multicoated with EVERCLEAR 5 Coating Technology to withstand almost any condition. Pure Harmonie filters are super lightweight for maximum auto focus performance and ultra-shallow profile to prevent vignetting. Considering all the engineering constraints Cokin had to take into account when making the thinnest Multi-Coated Anti-UV filter in the world, they have met the highest standards thanks to a extremely high quality glass with impressive transmittance. Anti-UV filters are used to prevent ultraviolet light from getting through the lens and helps reduce the haziness or fogging caused by this type of light. Anti-UV filters also offer physical protection from dust and other elements that could possibly scratch your lens. All PURE Harmonie UV MC filters are made with extremely scratch resistant glass with a very high level of light transmission. Thanks to their extreme thinness, PURE Harmonie UV MC filters also prevent lens flare that could occur when using traditional UV filters. All Cokin PURE Harmonie filers are manufactured with EVERCLEAR 5 Coating Technology which is a multi-layered coating. The 5 stands for the benefits of this coating on the filter: Water Repellent - Anti-Oil - Anti-Dust - Anti-Soil - Scratch Resistant. Another added benefit of this hard multi-coating is that the filter is very easy to clean. They are just perfect. They are PURE.