The Canon Drop-In PL-C 52 (WIII) Circular Polarizing Filter is the latest iteration of the Canon Drop-in Polarizing Filter. While Canon doesn’t specify any change in optical performance, the paint color of the filter holder itself has been updated to match the latest generation 400mm f/2.8L IS III and 600mm f/4L IS III lenses. Like the previous version of the Drop-In CP, it features the same dial on top that allows for quick adjustment of polarization.