Originally posted by causey b) above f5.6, and especially above f8, there is no visible corner softness with the Sigma.
unless when you compare it with the image taken by the DA12-24. as much as I want to believe this, which I had before I made some more comparisons, there is still some visible corner sharpness, most especially at 10mm. at 12mm, the results that I had seen are much better, although softness can still be detected. if small full image is taken, such softness may or can be very difficult to notice. full crops or anything larger would show the softness much more obviously.
the good thing about the sigma 10-20 however is that it is significantly cheaper (unless if you find a steal price for a used 12-24) and pretty good CA/PF control.