NiSi 72mm Circular ND Filter Kit | NiSi Optics USA
Amazon.com : NiSi 72mm Swift True Color ND-Vario | 1-5 Stops Variable Neutral Density Filter | Adjustable ND, True-to-Life Color, No Vignetting, Optical Glass with Nano Coating | Photography and Videography : Electronics
Tiffen 72mm Variable Neutral Density Filter
Platinum™ 72mm and 77mm Variable Neutral Density (ND) Lens Filter PT-MC400VND77 - Best Buy