Regarding the Sigma 12-24 I tested 5 and I can honestly tell you that the sample variations of the Sigma 12-24 was larger than any Canon lens. They vary from good to the feel of looking through a coke bottle. I have no idea how Steve Weldon can somehow tell you something different.
Well I did buy the Sigma 12-24 and have been very happy with this lens. Distortion is very low but it does suffer from CA.
Later when the Canon 16-35II arrived and I got to hand pick a sample, the sharpness and crispiness was so much better than the Sigma 12-24. I did come with a cost: more lens distortion and CA (this is easily corrected in post) I sold my 12-24 with no regret.
My advice to you is not to buy the lens unless you can hand pick a good sample.
It the early years of RG forum and LL forum bad advice regarding lenses cost me a lot of money. Listening to advice from people who raved about a certain lens and who spoke their case well, let to many frustrations since my standards regarding lenses was not in sync with what I read and got exited about.
Good luck,
TES
Tes - First, please don't misquote me. It's not appreciated. I never said the sample variation from Sigma was any worse or any better than Canon. I simply gave my experience with more than a dozen samples.
Second, I also recommended he go to a dealer and rent/try/borrow one and see if it met his standards.
Third, I find it very interesting that you were "very happy" with the Sigma 12-24mm.. until you found something better.. and then your 'standards' increased when a new lens came out on the market.. You were "very happy" before, but now you can "never be happy" again with that lens. I maintain this is a mentality we need to be careful of far more than choosing a bad lens. Its nonsensical in the extreme. Think about it.
Fourth, you didn't state at what focal lengths and apertures you claim the 16-35mm II betters the 12-24mm. Obviously it cannot better it at 12-15mm at any aperture. And in my experience with many samples the 16-35mm II is on par or perhaps a bit less at F8 or better. I haven't tried the 17mm TSE yet.. and stitching is an option.. but it does change the intended utility of the lens so I think this becomes about far more than a lens when you bring stitching into the equation.
Some have said you can't get good quality "large" prints from the 12-24mm and I think this cannot be claimed unqualified. I've made "large prints" for years from the 12-24mm. I say if someone buys your prints or the client is happy when he pays for your work.. then the lens did just fine. I don't have some abstract "personal standard" in my head.. I've never ever had someone point to one of my images from the 12-24mm (or any other lens for that matter) and tell me the print is unacceptable because of the lens.. or sharpness.. or any of the small pixel peeping details. I think it's silly to think someone would.
But yes, for sure Luis should see what images come from this lens and see if he'd be happy with the images. A quick look on the DPR forum today
shows this thread (and several others featuring the 12-24mm) showing some images from the 12-24 from a guy who knows how to use his equipment. He states he prints at 20x30 inches.. and looking at the images I believe him. I don't think anyone who considers themselves a photographer would look at these images and say "gee, that 12-24mm didn't do the scene justice" or something to that effect.
The 12-24mm in the right hands is going to take great images. Yes, there is probably sample variation. I just haven't experienced it and that should come as no surprise, a dozen samples is hardly representative. Yes there are probably better lenses available. Yes stitching would create more wide and detailed images. But there is nothing else out there that allows a 12mm view, that you can easily hand hold, and use to take great images. or 13mm.. Especially at this price point. Personally I'm not even sure a Canon 14mm prime will do 'better' at F8 or better. From 12-15mm it stands alone.. and from 16-20 it at least holds its own with anything else out there at F8 or better.
I can say this because I've used it for over five years and handled over a dozen samples of the lens and many times that many 16-35's and 17-40's. Of course the lenses you handled could perform differently.. it would be a more than a bit.. well.. weird.. to pretend I know how the lenses you used that I haven't seen performed..