Neutral Density filters have several uses and offer the possibility to achieve otherwise unachievable results. ND filters appear gray and reduce the amount of light reaching the film, they have no affect on color balance. The main uses of Neutral Density filter are: To decrease depth of field by allowing wider apertures to be used, which helps separate subjects from their background. To enable slow shutter speeds to be used, especially with fast films, to record movement in subjects such as waterfalls, clouds, cars, seas etc. To decrease the effective ISO of high speed film (ie: above ISO400) and allow it to be used outdoors in bright situations. To allow video cameras (which have fixed shutter speeds) to film subjects such as snow, sand or other bright scenes which would normally cause over-exposure.