zeiss 15 vs zeiss 21
i choose neither and would get the Nikon 14-24/2.8
I'm some one who shoots around 90% of my work within the 24-50 area. 24mm being where I begin to think its just tooooo wide but once in a while I'd be thinking I would do great with a wider for some rare situation and that would be the 21mm. a landscape-photographer surely will have another opinion, I'm a photojournalist.
On another note, currently I'm deciding on a wide for video work and I leaning over to the 18mm 3.5 side. having tested it, corners are way to distorted for my liking for stills but for video it might be perfect for me.
I'd imagine the key difference on 15mm to 21mm is that with 15mm you get the ultimate wide but you lack the ability to be able to select focus since anything put up front would be extremely distorted. with the 21mm you still get a wide angle and it has pleasing depth of field. but a need for even wider than 21mm makes the 15mm the obvious choice.
Sorry if it sounds obvious, but that's what should be driving the choice.
15 and 21 are VERY different focal lengths. The former is an EXTREME wide angle, which is VERY hard to put to good (i.e. non-gimmick) use, while the latter is still VERY wide for most uses, but considerably more versatile.
why would you select the 21 over the 15?
Any 21mm owner like me is likely oogling the 15. The price of the 15 could also be reflected by need, its expensive and so its FL must be of use. Cityscapes/landscapes very deep scenes and yet it could still be used for dramatic close focus and street scenes. I already shoot the 21 as a general purpose lens, at 15mm I'd be pushing it but can think of places it would be of use and would likely need to carry it on a 2nd body because its a lens at the extreme end and not what you would regard as general purpose.
I am not sure if I would like to go 15mm though, as it sounds too specific purpose. Whereas 21mm you can still pass it as general walk around lens... although it's more like journalistic style shots.
I now only shoot FX, I notice you post a lot on the DX forum.
When I had my D300, the most used lens was the Tokina 12-24 f4 which gave a field of view of 18-36 on DX. Great lens and worth considering for wide fans using DX. Sigma make some nice DX wides as well.
The reason I say this is not to go against Zeiss (I have two Zeiss, the 18mm and 21 mm) but the main reason to buy the 15 is for full frame coverage on FX.
Try this link to Nikon Lens simulator. Not completly accurate but a good representation of what you can expect with regard to angle of view on DX and FX.
You can never have enough angle for architecture and interiors to get the feeling of space and avoid keystone perspective distortion in tight urban spaces and large and high interiors like atria, churches, etc.
It takes 18mm to give you a 90-degree horizontal angle, just enough to take in everyone and everything in an entire rectangular room by shooting from one corner in landscape format.
15mm makes it wide enough to comfortably get all the walls as well.
The Zeiss 15mm f/2.8 is attractive to me because of its solid optics and the fact that it can take a screw-on filter. I like shooting in places like Yellowstone, where water spray is high in silica content. As awesome as the Nikon 14-24 might be, I'm uncomfortable shooting with a naked front element. Clean wides with a protected front? I'm saving my Benjamins. Gonna need a stack of em.
Switching to Nikon D800 from Canon EOS 60D
PowerShot S3, Casio EX-F1, FH100
Casio EX-F-One - http://marge.ragesw.com/~phyzorg/highspeed/