I would like to get a circular polarizer, but I'm not sure which one. I don't want a cheap one, but I don't want to spent too much more than $100 either. Also, I'm not sure what size to get. If I get a 67mm for my current lens, and then in the future I get a larger lens, I'd have to get another polarizer to fit that lens. Should I get a larger filter (like 77mm) and use step-up rings? This would cost more, but I would probably be able to use the same filter for almost any lens I would ever own. Any suggestions?