I bought a B+W (xs-pro KSM HTC) circular polarizer for my sigma 17-50 lens. I shoot with a canon t2i (550D). It screws on, and has a rotating element. in general it looks fantastic, definitely better than my last polarizer. But in the field, I can never tell the difference of the image when I spin the thing. Looking at the image on the computer I can tell right away that sort of... directionality (?) of the polarizer. But looking on live view out in the sun, or looking through the view finder I feel like I cant tell. Any tips for getting a handle on this while shooting?