Quote Originally Posted by jap View Post
That has nothing to do with the type of polarizer. As Darkesha pointed out, that's a consequence of dealing with medium wide (12-14mm) and ultra wide (11mm or less) lenses. The wide view, especially of the sky, can yield other-than-uniform contrast over the entire view.
Sorry, that's what I meant (I was referring to polarisers in general, just automatically wrote CPL...).

Thanks for the explanation anyway