EF Canon 10-22mm wide-angle zoom lens
If you’re a photographer using Canon gear and you intend selling your photos, then a Canon wide angle lens will prove an invaluable tool as the wide angle is arguably the most indispensable of all lenses.

In situations where a telephoto lens would be useful but you don’t have one, you can move closer to the subject or crop the image to fill the frame with your subject.

However, there is no comparable substitute for a wide angle lens. If you want your landscape to include foreground detail and distant mountains, you’ll have to move back a very long way to fit in the whole scene with a standard 50mm lens.

Canon EF16-35mm L wide-angle zoom lens
Similarly, when photographing tight interiors, there’s usually no space to move further back to include more of the scene, making it essential to use a wide angle lens.

If you use a Canon digital SLR camera such as one of the Canon Digital Rebels (Canon EOS 400D, 450D, 500D) or a Canon 40D or 50D, then it’s important to understand that these cameras are fitted with APS-C sensors that are smaller than a full-frame sensor. This has the effect of magnifying the image when using a normal Canon EF lens designed for use with 35mm cameras and is the same as using a 1.6x converter.

While this is great for photographers using telephoto lenses, it works against wide angle lenses, effectively making them longer - so your 24mm wide angle on a Digital Rebel becomes a 38mm (24 x 1.6) - almost standard rather than wide angle. To find out more about the impact of sensor size on a lens’s focal length, see Canon Digital SLR Crop Factor.