if you clicked on the link above that was posted there is a HUGE indepth review on the cannon lens u have vs the sigma 10-20 on cannon mount!
some points to note
*Both yield solid center and edge resolution performance with the Sigma slightly better.
*Distortion is present (especially at 10mm wide open) for both lenses but very acceptable being UWAs.
*Overall, these are 2 impressive UWA lenses with the Canon being IMO slightly better optically, though the build advantage goes to the Sigma. FWIW, I've reviewed countless full-frame captures of each lens both on screen (and printed out some comparison 11x14's), and by and far, it's EXTREMELY HARD to see any meaningful difference, save for the difference in color tone. If you shoot in RAW, it isn't an issue at all. Both lenses will satisfy as your UWA lens in your bag. And if you don't mind starting at 12mm, the Tokie is a VERY good one too.
so it says there is distortion and it says the canon is slightly better... however it also says The Sigma is 70% the cost of the Canon (and includes an EX petal-type hood and EX black carry pouch).
it also says
I spent a few hours early this morning, taking shots of various subjects, indoors and outdoors, and these 2 lenses are SO CLOSE IN RESOLVING POWER it's basically a wash. Both in center and edge resolution, the 2 lenses perform very similarly, it really depends on the specific accuracy of the AF on any given shot. Sometimes the Canon outresolves the Sigma, sometimes vice versa, the difference being the given AF accuracy of that particular capture. If I had to choose, it seems to me that the Sigma is slightly sharper (maybe 60% of the time, both in center and edge resolution),
Here is my analysis on the Canon 1022 (C) and Sigma 1020 (S). "10" being the best, "1" being the worst...
Resolution (center): S10, C9
Resolution (edge): C10, S10
Contrast: C10, S9
Vignetting: C10, S8
Distortion (barrel): C10, S10
Distortion (pincushion): C10, S10
Flare: C10, S8
CA: C10, S9
Build: S10, C7
Handling: C10, S10
Aperture (speed): C10, S9
AF (noise): C10, S9
AF (speed): C10, S9
MFD & Magnification: S10, C9
Widest FOV: C10, S10
Bang for Buck: S10, C7
10D/D60/D30 compatible: S Yes, C No
sigma out scores the canon the whole time...
i think i know more about photography than you do yes, i do this for my living... im paid to know what im talking about i also read reviews and do my research and listen to other people who know there s**t i dont just dismiss it because i feel like it...
photoguard do that because if your earning more than half your income through photography that means your in the public doing it often enough to need the public liability insurance!