Before we burn the barns in indignation lets get a couple of things clear:
- The Nikon 12-24 is a crop camera only coverage lens, a $1,099 crop camera only lens that doesn't do the "ultra wide" job half as well as the Canon 10-22 EF-s and that costs $599.
- The Nikon 14-24 is a FF ultra wide that costs $1,999. And those that herald it's all conquering capabilities probably haven't actually used it, yes it is much better than the Canon 16-35 f2.8 in the corners etc, but the 17 TS-E is a much better corrected lens for resolution, distortion and CA.
- The 17 TS-E has a coverage of 11mm if you do a horizontal stitch, the projection distortion from an 11mm to rectilinear on ff is pretty bad, virtually unusable most of the time.
Whilst I don't see 14mm as being a hard limit for ff rectilinear lenses, 11mm is beyond extreme, at these focal lengths a couple of mm makes a huge difference. The 16-35 f4 IS has confirmed Canon can make fine ultra wide zooms, but where is the market for an 11-24 f4 next to that 16-35 f4 IS? If it was f2.8 I'd probably buy it, but my most used lens is the 17 TS-E anyway so it would be a nice compliment to that, at f4 I can stitch the 17 to get 11 on the very rare occasions I need the fov. The 16-35 f4 IS appeals, but it has limited utility for me over the 17 TS-E.
I can see the market for an f2.8 ultra wide zoom to compliment the 16-35 f4 IS, and the kudos of going wider than the 14-24, I am sure Canon would like the title of widest ff rectilinear lens back too, but the Sigma 12-24 is an f4 so even a 12-24 f2.8 would give Canon the fastest widest ever (so far)........
Nikon's 14-24 f/2.8 weighs more than 2 lb. How much heavier would a well-corrected 12-24 f/2.8 weigh? Would a 3-4 lb lens sell?
I'm hoping that the Canon is working on a 16-35 f/2.8 III that is as easily filterable as the II. A 16-35 f/2.8 III, 16-35 f/4 IS, and a 11-24 f/4 will meet most photographers needs and would provide the best breadth of high performance lenses amongst mainstream camera/lens manufacturers. How will 11mm be used? I'm not sure, but I'm sure that people will figure out a use for it, and then it'll be copied ad naseum like the Go Pro action video or aerial/drone stuff...