B&W Kaeseman Circular Polarizer Multi-Resistant Coating (MRC) Slim Glass filters are constructed from specially selected polarizer foils with especially prepared optical glass. Completely edge-sealed, these Kaeseman encased series filters are designed for maximum durability under extreme climate conditions. Polarizing filters suppress disturbing reflection on mirrored surfaces like windows or water surfaces. As a result image information can be restored much better as the filters are used to select which light rays enter your camera lens, and saturate colors, providing better contrast. Varying the effect is accomplished by rotating the filter, the effect of which can be seen through the viewfinder. The filter factor varies from weaker to stronger according to the filter rotation and its orientation to the sun. The B + W series of slim line filters are intended for wide-angle lenses and are a mere 3mm thick to avoid vignetting. Thus the slim line filters do not have a front thread.