Neutral Density Filter: also known as light microscopy, gray density mirrors, neutral gray lens, its main function is to reduce the amount of light entering the camera, but will not affect the color of the original object, and can faithfully reproduce the scene of contrasts; ND4 available 2 files to reduce exposure, widely used in high altitude, sea and snow, and other outdoor shooting situations; Suitable for film cameras, digital cameras and camcorders.