However, clearly visible discoloration in the pictures at the highest setting. The corners are much brighter and meet all in the middle of an "X".
This of course also the parts of the image are dark that are not occupied by the "X". If you do not set the highest level, it is very faint and acceptable.
Since it was a very effective filter, I can live with this shortcoming. It should anyone be aware that you can only be limited with this filter work to ND 400 (rather only up to approx 300).