From the Manufacturer
24mm lenses are the entry into ultra-wide angle photography and this lens is the ideal starting point. It is extremely sharp and offers superior correction of linear distortion, and its f/2.8 aperture makes it easy to use with slow, fine-grain films or in low light. It focuses as close as 10 inches (25cm), and for many photographers gives the ideal combination of a wide-angle "look" without excessive perspective distortion.
Another superb ultra-wide-angle choice, with floating optics for superior performance throughout its focus range and a fast f/2.8 aperture that makes it a great alternative to a zoom lens for low-light shooting. Its rear-group focusing system reaches down to less than 10 inches (0.25m).
Wide and Fast
If you need an ultra-wide angle and a large aperture, one of the following lenses will fit the bill. Ultra-wide-angle lenses can capture scenes beyond your natural field of vision. The EF 15mm f/2.8 Fisheye, the widest of them all, has a 180∞ angle of view. For more normal-looking wide-angle shots, there are longer wide-angle lenses up to 35mm with the maximum aperture you need.
24mm wide angle lens for Canon cameras