The Sigma 105mm WR (Water Repellent) Circular Polarizer Filter helps to reduce reflections and glare by filtering out light that has become polarized due to reflection from a non-metallic surface. The light from the sun naturally becomes partially polarized due to reflecting off electrons in air molecules, causing the light to scatter into what appears as haze. A polarizing filter arranges, and filters, this directionally polarized light perpendicularly to the reflected light, allowing for the absorption of much of this light. This results in a noticeable reduction of glare and reflections from non-metallic surfaces and an increase in the saturation of skies and foliage.A circular polarizer only differs from a linear polarizer in that it contains a quarter wave plane in addition to the linear polarizing filter. The addition of this quarter wave plane is to circularly polarize the linearly polarized light for the use of auto focus and exposure functions. Due to how the light is broken down and filtered with a linear polarizer, auto focus and exposure accuracy become skewed during use. When the light becomes circularly polarized, it permits the use of these functions.This filter is multi-coated to eliminate internal ghosting and reflections. An anti-static coating serves to limit the accumulation of static electricity, making dust particles easier to remove or preventing them from adhering to the filter. Additionally, a water-repellent coating results in an improved beading effect when in contact with water, as well as oil, for greater cleaning efficiency while enhancing scratch resistance.Sigma WR Circular Polarizer filters are constructed from optical glass with a black rim. Set within an aluminum-alloy filter ring that can be rotated in order to adjust the intensity of the polarization effect, the glass provides increased clarity as well as color fidelity while the black rim further ensures that reflections do not occur along the filter's edge