Fotodiox Pro 186mm Slim MC-CPL Filter is a double threaded, multi-coated circular polarizer (MC-CPL) filter made of optical glass and featuring a rotating ring to allow for light ray selection. Remove unwanted reflections from non-metallic surfaces such as water or glass. CPL Filters are used to select which light rays enter your camera lens. CPL filters can also be used to saturate colors and to provide better contrast. The effect can be seen through the cameras viewfinder and changed by rotating the filter ring. The filter factor varies according to how the filter is rotated and its orientation to the sun or light source (approx. 0.3-3 stops). Typical applications include darkening skies and adding contrast to clouds, eliminating water reflection and window/glass/eyeglass reflection. CPL filters are specifically designed for use with auto-focus SLR cameras (They will also work on manual focus systems and video cameras without problems). The multiple lens coatings on the filter are designed to minimize unwanted color casts and reflections in your image for a sharper clearer photo.