20mm Wide Angle Lens Test

These photos were taken on a fixed tripod using autofocus on the centre of the image. These images are 100% crops from near the corner of the original.
	Sigma 20mm f1.8 EX DG	Canon EF-S 10-22mm f3.5-4.5	Canon EF-S 18-55mm f3.5-5.6
f1.8
f4
f5.6
f8
f11
f22
Summary
Sigma 20mm f1.8: For an expensive fixed focal length lens with fast maximum rated aperture, I expected a lot more from this lens. Stopped down two stops to f4 the image quality is still poor. This lens is out-performed by the cheap and standard Canon EF-S 18-55mm zoom lens even when it is wide open.
Canon EF-S 10-22mm: For an extreme wide angle zoom, image quality is quite good. In other tests, the performance from this lens has been even more impressive but here at this focal length it is apparently outdone by the cheaper 18-55mm zoom.
Canon EF-S 18-55mm: This is the standard kit lens sold with the Canon 300D and 350D (Rebel). However, image quality is excellent for such an affordable and compact lens.