Opteka 55mm HD Multi-Coated Variable Neutral Density (2-8 Stops) Fader Glass Filter The Opteka Variable Neutral Density filter is unique in the fact that it allows you to use just one filter to generate 2-8 stops of neutral density depending on how it is rotated Enables slow shutter speeds to be used, especially with high speed films, to record movement in subjects such as waterfalls, clouds, or cars Decreases depth of field by allowing wider apertures to be used, which helps separate subjects from their background Decreases the effective ISO of high speed film (above ISO 400) and allow it to be used outdoors in bright situations Allows cine and video cameras (which have fixed shutter speeds) to film subjects such as snow, sand or other bright scenes which could cause overexposure