these people do but be warned, they're REALLY picky bout every little thing. http://www.fredmiranda.com/reviews/showproduct.php?product=28&sort=7&cat=2&page=2
otherwise it's a wide. probably got pretty good optics considering it's price, it's USM which is kind of meh in my opinion on a wide cause i'd imagine it'd be pretty hard to misfocus often with a 20 on full frame. I guess it's not L which would probably be nice for snow shooting maybe. Not sure about distortion and stuff though but that link probably has info on it.