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 situations To allow cine and video cameras (which have fixed shutter speeds) to film subjects such as snow, sand or other bright scenes which could cause overexposure

Neutral Density Factors

2x = ND.3 (exposure adjustment = 1 stop, reduces ISO 1/2) 4x = ND.6 (exposure adjustment = 2 stops, reduces ISO 1/4) 8x = ND.9 (exposure adjustment = 3 stops, reduces ISO 1/8) As one of the premier filter manufacturers, Hoya filters continue to made from quality glass assuring the photographer clear, sharp and accurate images Hoya filters consistently provide even color all the way through the filter; All surfaces are ground and polished to specific thickness and tolerances