The Tiffen 49mm Digital ND Filter Kitis a complete set of filters to help you get better shots in bright light as well as assist you with some special effect images. Neutral density filters have several uses and offer the possibility to achieve otherwise unachievable results. They enable the shooter to adjust exposure without affecting color balance. ND filters appear gray and reduce the amount of light reaching the film. Determining which neutral density filter yields ideal results for any given lighting situation takes knowledge, experience, and a collection of such filters. Speaking generally, the 2-stop value (ND 0.6) effectively compensates average situations. Neutral Density Filters Have Four Main Uses To enable slow shutter speeds to be used, especially with high-speed films, to record movement in subjects such as waterfalls, clouds, or cars To decrease depth of field by allowing wider apertures to be used, which helps separate subjects from their background To decrease the effective ISO of high-speed film (above ISO 400) and allow it to be used outdoors in bright situation To allow cine and video cameras (which have fixed shutter speeds) to film subjects such as snow, sand, or other bright scenes that could cause overexposure Neutral Density Factors ND.6 (exposure adjustment = 2 stops, reduces ISO by 1/4) ND.9 (exposure adjustment = 3 stops, reduces ISO by 1/8) ND1.2 (exposure adjustment = 4 stops, reduces ISO by 1/16