Comments about Canon Canon 48 Circular Polarizer (Drop-in). Fits EF 200mm F/1.8L, EF 300mm F/2.8L, EF 400mm F/2.8L II, EF 500mm F/4.5L, EF 600mm F/4L:
once I found out this would work in my "manual focus" lens ( 300 2.8L and 800 5.6L) I couldn't wait to get it. (yes I shoot FILM) It was everything I expected and needed. Simple to use and works great.