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 colour or contrast. ProStop filters are a specialist range of high density ND's used to create motion blur in long exposure shots and can help create startling effects in water, cloud and other moving objects. This filter reduces the light by 1 stop. 85mm and 100mm (4") ProStops include a foam gasket which sits between the filter and the holder to help eliminate light leakage. Formatt-Hitech filters are made from the highest quality 1.5mm optical resin. The 85mm size is useable with the Formatt-Hitech 85mm holder systems or any 85mm (3.35"/ P Size) holder. The filter is also available in 67mm, 100mm, 150mm and 165mm sizes.