Formatt 4x5.65" (100x144mm) Glass Standard Neutral Density 0.3 - Neutral Density (or ND) filters produce a grey neutral effect and are used to reduce light in photography, enabling more control over exposure and depth of field without affecting color or contrast. ND's are made in different densities according to the level of light reduction from 1/3 to as much as 10 stops of light. The 0.3 ND reduces light by 1 stop.