QUOTE(tctham @ Jun 6 2012, 10:19 AM)

owh~ cuz i was reading somewhere about the sigma 10-20mm f/4-5.6 and some reviews say the lens is not overly sharp.. of course not expecting stellar performance, but they say the DOF is curved instead of being straight..
I can tell you wide open the Sigma it is not pin sharp. If you want sharp wide open, the Nikon AF-S 14-24mm f/2.8 is the one you should get. Even then, the 14-24mm f/2.8 is sharp in the centre and not sharp in the corners at f/2.8 wide open due to the wide curvature of the glass i.e. like what you mentioned DoF is not the same in the centre and in the corner. What more for a lens that is more than twice cheaper !
Anyway, why do you need a lens sharp wide open? Wide angle lenses for landscapes are usually stopped down to get DoF. By then, any erros due tot he lens curvature is taken care by the DoF from stopping down.
I'll post an example below that I took a while back and without looking at the EXIF, could you tell the difference between the two disregarding the slight WB and FoV difference? Stop down enough and you could not tell a difference at a glance.
» Click to show Spoiler - click again to hide... «
QUOTE(tctham @ Jun 6 2012, 10:19 AM)
so they say even though the objects lies in the parallel to the sensor.. the corner objects may not be in focus even though the centre object is in focus.. is this claim true? is it a deal-breaker in actual shooting? or am i just looking at very trivial problems? i actually interested in the tokina 11-16.. but my camera have no motor to test the AF.. otherwise need borrow people's camera to test during COD

Like I mentioned above, the best wide angle lens also suffer from slightly soft corners. More obvious if you shoot on a 36MP FX body. Not so obvious on the smaller MP D700/D3/D3s FX sensor and certainly not at all on a crop sensor because only the centre portion of the lens is used.
It is so difficult to get corner performance sharp like the centre. That is why good wide angle lenses cost almost the same as their tele counter part because it's more difficult to make a wide angle than a tele. This is why DX cropped sensors were made initially when digital cameras came out because DX sensors concentrates the centre part of the sensor and disregards the corner areas of the sensors which is most difficult to get correct.
QUOTE(zhinsara @ Jun 6 2012, 11:27 AM)
No filters for the 14-24 kind of kill it for me though. Got some ND and polarizers I occasionally use for landscapes on a Tokina 12-24 . Also, dat front element. But in my case I'm quite happy to sacrifice pure IQ in the form of primes for the speed and versatility of zooms.
There are custom made filters. Just that they cost a BOMB !
QUOTE(zhinsara @ Jun 6 2012, 11:27 AM)
You're the first to suggest keeping the wide end on DX actually

I never considered that.
The Tokina makes decent pics. If you're taking landscape pics and stopping down the lens, it is cheaper to go the DX route.
If you need a wide angle that is also a f/2.8 for shooting dark night clubbing scenes, the 14-24mm f/2.8 should be the one.
QUOTE(zhinsara @ Jun 6 2012, 11:27 AM)
Heh 1.4 and 1.8 lenses are nice to have, but using my 50/1.8D it's nearly always stopped down to 2.8 or 4 just for the DOF.
LOL, nice to have but most of the time it is not nice to the pocket.