Designed for the Phantom 4 Pro Camera, it replaces the UV filter that is pre-installed on the camera. Helps reduce the amount of light entering the lens to reduce glare and lower the Exposure Value.
Especially useful when shooting video to reduce shutter speed to double the frame-rate to introduce cinematic motion blur.
Put more simply, the ND filter helps avoid overexposed photos. The ND4 filter allows 1/4 of incoming light through, equal to a 2-stop filter. The ND8 filter allows 1/8 of incoming light through, equal to a 3-stop filter. The ND16 filter allows 1/16 of incoming light through, equal to a 4-stop filter.