The Heliopan Variable Gray ND Filter reduces the amount of light entering the lens up to 1 to 6 stops. It helps the photographer to control the depth of picture, which otherwise would be overexposed. This sturdy filter features a brass-mounting ring, painted in matte black that helps decrease reflections and increase durability. The front lens cap measures 77 mm. You can adjust the degree of light entering the lens by rotating the front filter ring and previsualize the amount of exposure required.