I just picked up a copy of the Canon 16-35, wanted to replace my 17-40 for the slight angle gain, and speed. What a disappointment. The center is sharp with good contrast but the corners are mush @ 16mm. I've read a wide variety of reviews on this lens, and they are all over the place. Are copy to copy variations that significant with the 16-35? Should I keep trying until I get a decent copy? I thought of going with a zeiss prime instead, the 18 or 21, but would rather have autofocus on all lenses. Any thoughts?