Please find below an image quality comparison created using 6 ultra-wide angle APS-C format lenses.
These images were captured under a clear sky with a Canon EOS Rebel T2i. RAW image format was used along with the Standard Picture Style. Sharpness was set down to "1".
Shown are 100% crops from a position very close to the lower left corner of the frame (the ISO 12233 image quality comparison tool uses crops from the center and the right side of the frame). The corner of the frame is typically where image quality is at its worst. The camera was positioned such that this scene remained in the same position in the frame for each lens/focal length change. Identical focal lengths are not always being compared - use discernment when comparing images with differently-enlarged details.
Back to the Canon EF-S 10-22mm f/3.5-4.5 USM Lens Review
Back to the Sigma 8-16mm f/4.5-5.6 DC HSM Lens Review
Back to the Sigma 10-20mm f/3.5 EX DC HSM Lens Review
Back to the Sigma 10-20mm f/4-5.6 EX DC HSM Lens Review
Back to the Tamron 10-24mm f/3.5-4.5 DI II Lens Review
Back to the Tokina 11-16mm f/2.8 AT-X Pro DX Lens Review