how does the canon EF-S 10-22mm f/3.5-4.5 USM work with a UV filter and a polarizer? If well, what polarizer should i look at purchasing. i dont want to spend a crazy amount but i want something decent enough. what should i be looking for when using an EF2XII extender with a EF 100-400mm f/4.5-5.6L IS USM. I'm seriously thinking of purchasing this lens and want to hear some opinion about the extender.