I wanted a large aperture and 24mm around the question was quickly made. There is the Canon EF 24mm f / 2.8 not open enough (as many keep zoom) and the Canon EF 24mm f / 1.4 L II USM. I would have liked to have it, but the price a bit crazy for an amateur discouraged me. This left only the Sigma and I was not disappointed. This is overall a good product that I recommend to those who can not or do not want to pay the Canon. Positives. The quality of construction, the grand opening, the image quality except in the corners at wide apertures (normal) and really usable macro mode, rare in a wide angle. Idyll unfortunately marred by a not so slow HSM autofocus and also this annoying maneuver to disengage autofocus. We must put the AF switch to Off, but in addition you have to pull the focus ring to M, there has been easier! There is also a slight focus forehead fairly common problem it seems from Sigma. I tested it from a friend who has the same behavior. You can mitigate this concern on boxes provided for fine adjustment of AF but on the other it is probably best to focus manually with large openings. But this difference AF is also quite common in Canon, even on L, so ...