I ordered a slip on Circular Polarised filter which came today, and fits really nicely, What I'm not sure about is how to know the best angle to position it, as obviously it can vary from fully blocking to open as you rotate it. Do people look through the filter held in fingers at the likely scene and rotate to find best position for that time/day then slide onto camera at that position, or is there a std position you stick with, ie mark the filter top fully blocked (or some proportion?) and stick with that every time? Any tips would be great as I'm completely new to CPL filters !!