Update on 06/05: If the exposure is correct, the image is sharp at ANY focal length. Greatest lens for landscape and portrait. There is no dark corner and no distortion.Having the lens for 5 days, I am very happy with this lens. This is my first L lens and it is much better than any of other lenses. The lens was put on my XTI camera. I ignored all the comments that this lens does not match this camera. What I wanted to do is to get nice pictures on the camera on hand. Widness is not the only issue to measure the quality of the lens. I uploaded one picture and definitely that is not the best picture because I am still improving my photographic skills.Bought $1350 at Buydig with a $150 Heleopan UV filter.