Amazon.com : JJC 2-in-1 82mm Variable ND Filter & CPL Polarizer Filter, 5 Hard Stops ND2-ND32 Adjustable Neutral Density Filter, Including Moistureproof Storage Case and Lens Cap : Electronics
Using a variable ND (natural density) filter in photo and video - YouTube
How Does a Variable ND Filter Work?
Ideas for Using a Variable ND Filter to Control Landscapes | PetaPixel