Hey folks, I just got a Tamron 17-50 2.8 lens, and I have the Cokin Pro-Z filter holder for my 4x6 ND grads. What would YOU do if you wanted to get a polarizer. I was gonna get a CPOL that screwed onto the lens, and then mount the filter holder on that, but I also heard recently about something called a sprocket polarizer, which can be mounted in the filter holder. I was kinda just thinking about getting the Singh-Ray Vari-ND Duo, which is a variable ND filter and CPOL in one. Thoughts?