Neutral density (or ND) filters produce a neutral grey effect and are used to reduce light in photography, allowing better control of exposure and depth of field without affecting colour or contrast. NDs are manufactured in various densities depending on the level of light reduction, ranging from 1/3 up to 10 stops of light. The ND 0.3 reduces light by one stop. The filter is also available in 100mm, 144mm, 127mm and 168mm sizes. Formatt-Hitech glass filters are manufactured from the world's highest quality optical glass, Schott Superwite. Features: Standard 4x5.65" (100x144mm) neutral density glass filter - Manufactured from the world's highest quality optical glass, Schott Superwite - Manufactured in the UK using the world's most advanced computer-controlled filter manufacturing technologies.