This is probably something simple, but it's my first variable ND filter experience, and it ain't going so hot so far. I stopped this morning on the way in to work, set up a tripod, put the 14 on the XT, and took this. I noticed it on the rear LCD, and thought "uh oh. Maybe it's just on the LCD and won't be on the image?" But of course it is. Lightening up the ND filter to around 4 stops, it diminishes but isn't gone... So what causes this? I know about circular vs linear polarizers, but have never heard of ND filters having the same potential issue.