Amazon.com : K&F Concept 67mm Variable ND Filter ND2-ND32 Camera Lens Filter (1-5 Stops) No X Cross HD Neutral Density Filter with 28 Multi-Layer Coatings Waterproof : Electronics
Ron Martinsen's Photography Blog: COMPARISON: Variable Neutral Density Filters (Singh-Ray, B+W, Hoya, Tiffen & Bower)
Our Favorite Neutral Density Filters | Gear Talk Episode 5
8-STOP VARIABLE ND FILTER(58mm-82mm) – Official 7Artisans Store