Firstly Hello, this being my first post. Now to my issue - I use a Lee polariser with a wide angle adapter ring and no other filters on both my Canon 17-40mm and my Sigma 24-70mm F2.8 and I get vignetting with both. I notice a lot of people (including Joe Cornish) using the Heliopan polariser which fits the Lee holder but which is supposed to be thinner than the Lee. Does this make a difference to the vignetting problem?