Is this for use with the 16-35mm f/2.8L II? The 82mm diameter makes me suspect so, and there are a few additional considerations when using a CP on a wide angle lens. First, you may need to use a thin profile filter in the case of the CP, as a standard type may vignette at the wide end - especially if stacked with a second filter such as a UV. And secondly CPs can be problematic with ultra-wide lenses, since the polarization varies across the wide angle of view and can make skies look patchy and uneven. There was a good thread discussing this recently:http://www.canonrumors.com/forum/index.php?topic=8112.0
Buy a B+W AUC Zirkular-Polfilter Käsemann with MRC-sealing
It delivers a perfect picture quality.
I own the B&W BWKCPMCS77 slim 77 mm Kaesemann MRC CP, which I purchased a few months ago. I love B&W filters and use them on all my lenses, but I can't say I recommend this model. It is
very thin and I don't get any vignetting on my 17-40mm f/4L provided I don't stack filters (when stacked with an F-Pro UV I get just a touch of vignetting at 17mm on my 5D2). But the thinness has its disadvantages. It makes the control ring difficult to adjust because there is not much to grab onto, particularly if a lens hood is fitted. It also means that a conventional lens cap does not work since there are no internal filter threads. The supplied special cap invariably falls off when I put the lens in my bag, making it essentially useless.
These complaints are repeated over and over in the B&H user reviews, but I could live with them as tradeoffs for the lack of vignetting. However, while using this filter in cold weather at Bryce Canyon NP in Utah, it frequently became jammed on my UV filter. I think this is because, unlike my other B&W filters which are brass and don't get stuck, this CP is made of steel - presumably brass is too soft to use for a thin profile filter. Finally it jammed permanently, and nothing I have tried has succeeded in freeing it. I was planning on selling it and going with a grad ND setup instead, but I can't do that until I can separate it. Very disappointing from an otherwise excellent brand...
Any advice on separating jammed filters would be much appreciated
I don't think it is cross-threaded, but filter wrenches don't work, even when used with elastic bands for better grip.