The Hoya Pro ND4 filter has a 2-stop light reduction. This enables the photographer to gain 2 f-stop that allows them shoot at a wider aperture resulting in a shallower depth of field. The ProND filters use ACCU-ND coating which is exclusive to Hoya's clear optical glass. This metallic ACCU-ND coating on the front and back ensures the filter does not colour shift as you change ProND filters. The ACCU-ND coating in the Hoya ProND filter yields a truly neutral colour balance that will NOT add any noticeable colour cast to an image. This filter is aimed at still photographers as well as videographers in the HDSLR video market.