Amazon.com : Hoya 82mm Variable Density Screw-in Filter : Camera Lens Neutral Density Filters : Electronics
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
Ron Martinsen's Photography Blog: COMPARISON: Variable Neutral Density Filters (Singh-Ray, B+W, Hoya, Tiffen & Bower)