"The Hoya Neutral Density (NDX4) 0.6 Filter has several uses and offers the possibility to achieve otherwise unachievable results. ND filters appear gray and reduce the amount of light reaching the film. They have no effect on color balance.

Multi-coated to minimize reflection at the filter surfaces which reduces flare and ghosting.

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 be 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"