I see you have quite a kit in the wide end of things, and I really enjoyed the 12-24 as well. I was just about to buy another copy when I saw the 11-24 rumor and decided to hold off to see if it was real. I have one on pre-order and I'm sure it will be incredible, but 3x as good as the Sigma? Probably not.
one more recently @12mm f4.5 on a 1DsmkIIIInteresting shot and beautiful engine. I bet there's going to be a lot more interest in this lens once the 11-24 hits the streets.
in interior settings and avoiding bright conditions outside, this lens shines without flare (pun intended)
The new canon will have to be an outstanding corner and flare performer along with low coma, to justify me purchasing it - I am tempted, very tempted, but will behave and wir till all the dust settles as I am very well served with my UWA arsenal...
So big question...how does the new Canon compare and did you have a mk 1 or mk II of the Sigma?
I had the Mk II of the Sigma and here are the differences that I've noted:Negatives for Canon
-Canon is MUCH more expensive, but like most things, it's not actually 3x better
-Canon is MUCH bigger and heavier, to the point of just barely fitting in a standard camera bag
-Canon is very front heavy
-Canon lens cap scratches the hood (not a huge deal)
-Canon is also soft in the extreme corners, though only the very last 10% or so vs. 20-30% for the Sigma
-AF seems about the same (not really a negative), but I don't use AF much on lenses this wide
-Canon includes a lousy lens "pouch" versus the nice, padded and foam case Sigma includes. They really should have included a lens case like the 70-200 f/2.8s, 180 macro, and 300 f/4 IS/400 f/5.6 lenses for the price.Positives for Canon
-Canon is far sharper wide open and visibly sharper stopped down as well. In the center 2/3 of the frame, it gives the 24-70 II and many other lenses a run for their money.
-Canon is sharp at all focal lengths - Sigma was sharp at 12mm, but not great at other FLs
-Contrast is quite a bit better on the Canon
-Distortion is a bit better, but not considerably so - probably similar to the Sigma Mk I
-CA is definitely lower, but not completely absent
-Vignetting seems lower as well
-Canon has some small flare, but it's harder to flare and nearly impossible to get veiling flare
-1 more mm
-Switches are recessed on the Canon
-Lens cap locks onto the lens
-(Likely) better resale value. I sold the Sigma in mint condition for 1/2 of what I paid for it!
So overall, I would say that the Canon is definitely a better lens, but only for people who are going to use it a lot. For hobbyists, infrequent users, or people interested but unsure about ultrawides, the Sigma, especially a used one in good condition, is a steal in comparison. I have sold many 20x30" and a few 40x60" prints shot with the Sigma and would have no reservations recommending it. If you own one of the Sigmas, especially the Mk I, the Canon is definitely going to be a worthwhile upgrade if you will get a lot of use out of it and can afford it without breaking the bank.