I feel that the sigma does not have very strong CA. It is minor though but present as with many wide angles. Certainly very acceptable for £300. If you check my sample shots you'll be able to see exactly what I'm talking about.
If you don't mind my chiming in, I feel like the siggy has less CA, and sharper images than the canon, but I feel like my photography has improved immensly in the six months between my using the 10-22 and the 10-20
I've no experience of the alternatives, but i can say i've been very happy with canon 10-22mm. Not noticed any resolution problems or purple fringing except where i'd expect to see it (green leaves against blue sky). I also have a 17-40L which i've used on a full frame (1dsmk2) and comparing the two i'd say that the 10-22mm on crop has much better corner distortion characteristics and corner sharpness than the 17-40mm on FF. To pitch in with some examples, these were all taken on 350D with the 10-22mm:
have no right to upload a picture of me at this forum without my permission. I hope his retirement. When you want to upload some of my own ask permission. Otherwise there are laws for this ...
