BW gray filters are available in a number of values 1 2 3 6 & 10 f-stops & permit wide aperture even when it is very bright for low depth of field & an interplay of sharpness & blur andor long exposure times for motion blur or wiping effects speed emphasis or flow of water. They also permit normal time values & f-stop values when the film sensitivity is too high for the prevailing light. Gray filters with higher density 3 to 0 f-stops are also used for technical photography e. g. shots of lit lamp filaments of combustion processes & procedures in melting ovens as well as for astrophotography. br STRONGCAUTIONSTRONG These filters must not be used for the direct visual observation of the sun they can cause severe burn to the retina up to total blindness since they transmit too much infrared for this purpose special dielectric solar filters & Astro Solar Film are available for this. 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. Extra-Slim Mounting Rings that Eliminate Problems Associated with SLR Wide-angle & Telephoto Imaging The BW standard filter mount F-Pro provides some substantial enhancements over the previous BW sta