Summary: ok, so i got this lens because i wanted a compact wide angle lens that i could easily throw in my bag to cover events. however , i was greatly disappointed with the lens. it vignettes like there is no tomorrow, even using profile corrections on photoshop wont get rid of all the vignetting. PLUS this vignetting is not a pleasing vignette. its dark, ugly, and what it does is under expose images by more than a stop. another major issue is image quality.
Excerpt: I use AF and MF shooting the same subject, and MF is OK but not AF. Why? Is it the lemon I bought or it is the general situation that Canon only pay attention to more expensive L-lens. Then, how come Canon never think about to make 20mm L-lens? It is a big gap between 14mm and 24mm L-lenses.