Neutral Density Professional Photography Filter Set
Amazon.com : NEEWER 67mm MRC Variable ND Filter ND2-ND400, Neutral Density Adjustable ND Filter (0.3 to 2.7,1 to 9 Stops), Multi Layer Coated Optical Glass, Water Repellent & Scratch Resistant Ultra Slim
Singh-Ray 100 x 150mm Galen Rowell Graduated Neutral Density
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Amazon.com : Neewer 67mm Variable Fader ND Filter Neutral Density Variable Filter ND2 to ND32 (1-5 Stop) for Camera Lens NO X Spot, Ultra-Slim, Weather-Sealed : Electronics