I have the B+W 77mm Kaesemann Circular Polarizer Multi-Coated Glass Filter, which I am very happy with, I guess in the 72mm range it would run you about 145 dollars on amazon. I would almost suggest to get a larger filter, since you might want to buy a lens with a larger filter thread at a later time. Then it is easy to just use a step down ring and use the same filter for multiple lenses. My 77mm filter serves also my 72mm lenses in that way.
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