Camera: Canon EOS 10D
Primary Use: Wide Landscape Photography
This lens could use some improvements. If you're really looking for the widest possible rectilinear lens, then this is your answer. I really see no point in making this a zoom. The lens could possibly benefit from it by just being a single-focal 12mm.
Image quality: 3/5 (It's decent, but not mind blowing. Be careful of lens flare. Vignetting occurs when using the filter mount. Barrel distortion, but I actually like that).
AF speed: 1/5 (Pathetic AF speed considering it holds the HSM designation. Speed is SLOWER than Canon's non-USM motor).
AF acquisition: 4/5 (Still hunts, but in extreme cases).
Design: 3/5 (Filter mount will get too loose that eventually, it will not lock into place. Don't like the fact that the front element moves when zooming.)
Build quality: 3/5 (It feels cheap. I hope other EX lenses are not like this.)
You do not buy this lens because it can also cover 17mm and 24mm angles. You buy this lens for its 12mm capability. Nothing else.