The B&W 49mm Kaeseman Circular Polarizing Multi-Resistant Coating (MRC) Glass Filter (Slim) is constructed from select polarizer foils and especially prepared optical glass. Kaeseman ("encased") filters are completely edge-sealed for maximum durability under extreme climatic conditions.
Polarizing filters are used to select which light rays enter your camera lens. They can remove unwanted reflections from non-metallic surfaces such as water or glass and also saturate colors providing better contrast.
The effect can be seen through the viewfinder and varied by rotating the filter. The filter factor varies according to how the filter is rotated and its orientation to the sun.
B&W slim filters are for wide-angle lenses and are 3mm thick. They do not have a front thread.