NiSi ND Filter for True Color VND and Swift System (77mm, 4-Stop)Introducing the NiSi ND16 4 Stop Filter for the NiSi True Color VND Swift System that expands the NiSi True Color 1 to 5 stop VND variable filter to a 5 to 9 stop VND when the bright conditions require more stops. Expanded Capability The NiSi Swift System works seamlessly with the NiSi True Color 1 to 5 stop VND variable ND filter allowing the capability to be expanded by adding extra filters simply by pressing them on the front of the NiSi True Color