The NIR-ND1.8CPL round filters are a special series of threaded filters from NiSi. These filters combine the enhancements from a circular polarizer with a 6-stop reduction in overall light to balance colors, increase depth-of-field, lengthen exposures and reduce reflections on non-metallic surfaces, all at the same time. Each filter also has a matched female thread on its face, to allow for filter stacking.