The Zeiss ZE 21mm f/2/8 Distagon for Canon EOS has been out of stock regularly, no doubt due to very strong demand, but B&H is now taking pre-orders, which means that they expect some to show up soon. It’s also available for Nikon as the ZF.2 model.
The 21/2.8 Distagon is a true standout, there really isn’t anything like it. I strongly advise anyone who likes ultra-wides to obtain one as soon as feasible. It is optically identical on Canon and Nikon and Pentax.
Today I was asked which lens to choose if the budget afforded only one lens, the choices being the Zeiss 100mm f/2 Makro-Planar or the Zeiss 21mm f/2.8 Distagon. Although the 100mm f/2 Makro-Planar is an exceptional lens, I do feel that a 21mm will see wider use for most shooters than the 100mm. It all depends on your preferred subject matter, but my default suggestion is to go with the 21mm as being more versatile indoors and out.
The Zeiss 21mm f/2.8 Distagon is very highly corrected for color aberrations and other problems, with near-macro close-up performance also. I show many examples on Canon and Nikon my my Guide to Zeiss ZF / Zeiss ZE Lenses.
As a friend of mine said when I loaned mine to him for a few hours: “I can’t make anything that looks like that with my Canon 16-35!”.
Although I own the Nikon 14-24 (excellent lens), I rarely use it, as I prefer the ergonomics and brilliance of the Zeiss 21/2.8. The Nikon 14-24 is best used for autofocus and when the shooting demands rapid adjustment of angular coverage.
On Canon EOS, it’s no contest, my EF 16-35/2.8L II has sat unused for a long time. While the Canon EF 24/1.4L II is excellent, it has some drawbacks, see my review in DAP.