ND filter is like having sunglasses for your drone camera. ND filters reduce the amount of light that goes into the lens, which results in a lower shutter speed. This gives shots more motion blur and also helps cut down on micro-vibrations that could show up in your videos.
There are three different ND filters for DJI drones that you can get. ND4 is the brightest and ND16 is the darkest (creating more motion blur).
The number associated with an ND filter indicates that how much light enters the lens in terms of a fraction:
In most situations you can stick with ND8, but when the sun starts setting, don’t forget to switch back to the original filter that comes which comes with your drone (in most cases with DJI Mavic Pro, Spark, Inspire 1|2 and Phantom 1|2|3|4 drones), or all your shots will start looking dark and grainy.
Popular ND Filters for drones: