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.
Mounted within a non-threaded, steel filter ring, this filter is made specifically to fit within a separately available Kase 90mm Magnetic Lens Adapter Ring behind a Kase K9 100mm Filter Holder. Constructed from Schott B270 Superwhite glass for enhanced clarity and color fidelity, each glass surface includes multiple layers of anti-reflection coatings to prevent internal ghosting and reflections. These coatings also offer greater protection to the filter substrate and help it to stay clean for longer than with uncoated filters.