I just bought a brand new B&W 6 stop ND filter. Took pics with it. The images end up being under exposed by 2/3 to 1 stop and I have to dial in about 1200 deg C more color temp to restore white balance (the filter is cool).
Oh, and the corners show more light fall-off with the filter than without. This is with UWA lenses. I haven't tried with normal or tele focal lengths.
Is all of this normal???