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.
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.