[Klaus]

Looking at the images, I notice something that I have noticed in the past with my Tokina 12-24mm d4 DX: it is as if the lens has a "built in pol. filter". I mean that the sky looks darker blue than usual when not using a pol.filter.

I can recognize the similar effect too - appeared on my 12-24 and 11-16 MK1, but not at Tokina 100 Macro.

This is not a PL-like effect - it's just called the Sydney sky here ... ;-)