The Neutral density kit contains the 3 most widely used ND densities – 0.3 (1 stop), 0.6 (2 stops) and 0.9 (3 stops). Neutral Densit (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. NDs are made in different densities according to the level of light reduction from 1/3 to as much as 10 stops of light. This 150mm filter kit is useable with Lee 150mm holder systems and other similar 150mm holders. The kit is also available in 85mm, 100mm and 165mm sizes. Hitech filters are made from the highest quality 1.5mm optical resin.