Polarizing filters make it possible to reduce reflections in cases of oblique light incident on electrically non-conductive surfaces e. g. glass plastics varnish & increase color saturation. Circular polarizing filters have the same effect & also prevent incorrect exposure times & autofocus errors of cameras with an beam splitter in the TTL exposure meter or AF beam path. Why BW over other filter brands. BW filters have been made with Schott glass which guarantees the very highest glass quality. Good quality cameras & lenses are a major investment & at BW we believe that if you should have the best quality filters. Theres no point in buying an expensive optically superior lens only to put a piece of inferior glass over the front of it BW filters are also coated with state of the art coatings BW are the first filter manufacturer in the world to offer multi resistant coatings MRC. The coatings are extremely low-reflective & highly resistant to scratching but above all the unique dirt & water-repellent surface makes cleaning the filters easier. BW filters all feature brass mounts designed to fix the high-quality filter glass in position for life. Brass mounts wont bind with your lens thread or other filters a major advantage over cheaper filters.