Freewell FWH9B-ND4 Overview Control the light input on your GoPro HERO9 Black action camera with this ND4 Filter from Freewell. The Freewell 4K series filter is designed to darken the image, to help you control exposure when capturing photos or video outdoors. The ND4 filter cuts the amount of light hitting the camera sensor by two f-stops, allowing you to shoot with a wider aperture or slower shutter speed than normally required. The filter is coated to prevent dust, scratches, water, or oil from accumulating on your lens, and it features an efficient bayonet-style design to replace the original front lens element. A magnetic case is included to store and transport the filter. Compatibility GoPro HERO9 Black action camera ND4 Neutral Density Filter The ND4 filter helps slow down the shutter speed by two f-stops. This is excellent for capturing crystal-clear video when the weather is overcast or fairly cloudy, with lower daylight. Use of them does not imply any affiliation with or endorsement by them.