The Sigma DG Circular Polarizer Filter helps to reduce reflections and glare by filtering out light that has become polarised due to reflection from a non-metallic surface. The light from the sun naturally becomes partially polarised due to reflecting off electrons in air molecules, causing the light to scatter into what appears as haze. A polarising filter arranges, and filters this directionally polarised 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 general increase in contrast becomes visible as well.A circular polarizer only differs from a linear polarizer in that it contains a quarter wave plane in addition to the linear polarising filter. The addition of this quarter wave plane is to circularly polarised the linearly polarised 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 metering accuracy become skewed during use. When the light becomes circularly polarised, it permits the use of these functions.This Sigma DG Circular Polarizer Filter is coated to repel water drops and resist smudging from fingerprints. It is also treated to exhibit antistatic properties to prevent microscopic dust fromclinging to the front surface. This helps to ensure sharp images.- Helps to reduce reflections and glare by filtering out light that has become polarised due to reflection from a non-metallic surface- Polarising filters arrange, and filter directionally polarised light perpendicularly to the reflected light, allowing for the absorption of much of the light- Clears up haze in distant landscapes and provides more saturated, vivid colours- Strongest effect when used at a 90 angle from the sun- Circular polarizers are ideal for use with digital cameras and autofocus lenses where a linear polarizer will often disrupt auto exposure and focus features- Constructed from water, oil, and static resistant glass