Well, the ND filter simply does its job. It gives me a lot more control over the 16mm f/1.4 lens from Sigma, which is an excellent piece of glass. Since it is a fast, wide angle lens, there can be challenges which are easily dealt with using an ND filter. I did read the comment from a reviewer that mentioned an dark "x mark" across his image. I had to see if I could replicate it with this. I cranked the filter way past what I would have normally set it for, and was able to see the x as well. Neat. It's easily fixed though. Just don't "crank" an ND filter further than is necessary. I have a feeling that most all of them will exhibit the same characteristic, so it's just a matter of operator procedure to see that it doesn't happen. Honestly, I had never noticed it, simply because it was a setting that was never called for, given any of the lighting conditions I was shooting in. I can go to manual settings on my camera, and get a blacked out image, if I push the settings into "deep space", but why would I? Otherwise, the filter shows good edge sharpness, and no detectable distortion, but I'm not terribly picky. It gets rid of what problems I might have had with a high speed, wide angle lens, which is what I bought it for. Nice ND filter, and I'd buy it again.