The hoya 77mm pro nd 4 filter absorbs the light entering the lens evenly across the visible spectrum and reduces the light entering the lens by up to 2 fstops without affecting the colour balance reducing the amount of light allows the use of wider apertures and slower shutter speeds for creative and dramatic effects nd filters are widely used by landscape photographers who want to capture smooth flowing waterfalls or seascapes but still retain the correct exposure throughout the whole photo