As always, quality is expensive.
I have had a few cheap ones, but had serious problems with vignetting. Probably because they are significantly thicker then the slim versions from B&W and HOYA that I use.
On the 16-35 L the difference is just shocking. I don't know why the thickness of the glass has such an impact.
Hope this helps
Very much, thanks. (And to the others, as well.)
The cheap polarizing filters are a great value. It's like getting two filters in one - not only do you get a polarizing effect, you also get a great soft focus effect that reduces the sharpness of your image and provides a soft glow around your subject, and you get that soft focus effect for no extra charge!!Right on! ... sort of a Hypstamatic or Instagram effect for DSLRs!