Cokin PURE Harmonie filters are the thinnest and the lightest in the world. With a thickness of 4.5mm, they are almost invisible when mounted on your lens. Their weight is so light that you won't even notice that they are attached. Cokin PURE Harmonie filters have been engineered with no compromise: very robust, compatible with all lens caps. Super lightweight for maximum AF performance and ultra-shallow profile to prevent vignetting, they are just perfect. They are PURE. Circular Polarizer filters are used to reduce reflections from non-metallic surfaces (windows, water and so on) and increase density within the sky and/or foliage by absorbing reflected light. They also allow to emphasize details such as clouds and makes pictures crisper, with deeper color tones. Their effect cannot be achieved with a computer software.