The Sigma 49mm DG 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 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 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 metering accuracy become skewed during use. When the light becomes circularly polarized, 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 from clinging to the front surface. This helps to ensure sharp images.