Summary: I use this lens on a full frame camera (D700) - so the review is geared for full frame users. There are wider choices (with relative advantages / disadvantages) on the cropped sensor side - don't get this lens for DX. Pros: - the widest rectilinear lens for full frame.
Summary: I am just not satisfied with the IQ it is heavy and big and not that great compared to many super wide angle such as the fisheye The IQ gets better when I stop down to f8 and f11 so think carefully before you get this lens
Summary: I have had this 12-24 wide zoom for a while now and my opinion of this lens is improved. It is growing on me. The review I wrote below is true enough, but it is pretty understated. I must say I'd give this lensanother star after using it for a while.
Conclusion: It sure would be nice if Sigma had just made a good 12mm prime and let it go at that. For anything beyond 12mm I use my 17-40L. And it's too bad Canon doesn't offer a really good 20mm prime.
Pros: Half of this lens is great. Very sharp for the money. Very little distortion. The right side of my images are terrific.
Cons: The left half of my images are soft. I returned my first copy to Samy's (with some grumbling on their part) and the second was just the same. Good on the right, bad on the left.
Conclusion: If you want wide, this will give you wide. In fact, for those that shoot the Canon 1 series, your only choice for ultrawide zoom is this one. I don't use this lens very often, because it's rare for me to need to shoot that wide, but when I need to get an entire room into a shot, or need anything...
Pros: It sure is wide! Feels quite sturdy.
Cons: Stupid rear filter design. All my other lenses are sharper.
Conclusion: I use this lens pretty much as a 12mm prime, I hardly ever touch the zoom ring. I also shoot almost exclusively at F11 - F16. F16 seems to be the sharpest stop. The lens was a bit larger than I expected, it doesn't fit in my camer bag (it comes with it's own bag though).
Pros: solid construction, great feeling controlls good performance at F16, not much distortion
Cons: not very sharp anywhere near wide open, a bit tricky to use
Conclusion: 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.
Pros: Wide angle capability. Nice case.
Cons: It's a zoom - Sigma should have just focused on making it a wide prime. Bad design on the filter mount. Sub-par finish feel for a pro lens. Front element moves when zooming. Uber slow AF speed. Mediocre image quality.
Conclusion: I've had this lens for one weekend for testing. First I was VERY disappointed when I saw my studio photos of a resolution chart: unsharp corners, a LOT of chromatic aberations in the corners, average sharpness.
Pros: Extremly wide (12mm), quiet focusing (HSM), nice color rendering, average/good focusing speed, in the center relatively sharp for such a wide lens
Cons: not very sharp in the corners (even stopped down), a LOT of chromatic aberations in the corners, very large (82m) thread size