Compare Hoya 72mm Variable Neutral Density Filter vs Haida 72mm NanoPro Variable Neutral Density 1.2 to 2.7 Filter 4 to 9-Stop vs NiSi 72mm Variable Neutral Density 0.45 to 1.5 Filter 1.5
Compare Hoya 67mm Variable Neutral Density Filter vs Haida 77mm Pro II-S Super Wide-Angle Variable Neutral Density 0.9 to 3.0 Filter 3 to 10 Stops vs Hoya 72mm Variable Neutral Density Filter vs Tiffen 77mm Variable Neutral Density Filter
Here are 12 ND filters compared for color and sharpness - DIY Photography