This Drop-In K-Series Circular Polarizer Filter from H&Y Filters is made specifically to fit between a separately available H&Y Filters 100mm K-Series Filter Holder and one of the filter holder's adapter rings. When in use, this filter can help 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.

The Drop-In K-Series Circular Polarizer Filter is constructed from Schott B270 glass for increased optical clarity and color fidelity. It is mounted within a geared aluminum alloy filter ring assembly with an external dial, which allows for the independent rotation of the filter in order to adjust the intensity of its polarization effect. Each side of this filter includes eight layers of anti-reflection coating to prevent internal ghosting and reflections as well as an anti-smear nano coating for an improved beading effect when in contact with water or oil for greater cleaning efficiency.