Amazon.com : Tiffen 72mm Variable ND Filter ND & Digital HT Multi Coated UV Protector : Electronics
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MMX 72mm ND Vario 2-400 Variable Neutral Density Filter | eBay
NiSi 72mm 5-9 Stops Enhanced Variable ND Filter
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Amazon.com : NiSi 72mm Swift True Color ND-Vario - Variable Neutral Density Filter 1-5 Stops (ND2-ND32) - Rotating Adjustable ND, Compatible with NiSi Swift System Filters - Optical Glass, Waterproof Nano Coating : Electronics
Rent a Heliopan 72mm Variable ND Filter - BorrowLenses.com