Wideangle lenses make subjects appear further away and, as a consequence, smaller, than they do to the naked eye. They are useful when you can't stand back far enough to get everything you want in shot, such as when photographing a large building, an expansive view or large group shot. But they also produce an apparent perspective distortion in which subjects close to the camera can appear disproportionately larger than those further away - an effect that can be used by the photographer in all sorts of creative ways. They also give the illusion of placing the viewer in the thick of the action, which makes them popular with reportage and street photographers. Other hallmarks of wideangles include their ability to exaggerate lines and curves, and in some situations distort them, and to produce greater apparent depth of field at a given aperture than longer lenses. The more wideangle the lens, the more pronounced these effects will be.
Although wideangles are available in various fixed focal lengths, our recent tests suggest that a good wideangle zoom, covering a range of focal lengths, is often the smarter bet. Optically the best ones are on a par with many premium primes, they're often hardly any bigger and they may even cost less.
Wideangles are ideal for scenic views where their ability to include both foreground and background elements, and get both in focus, is very useful. Note how in this shot of Venice (shown here) which was taken using a Sigma 10-20mm lens on a Nikon D300, the gondolas are emphasised in size and importance, relative to the buildings. This perspective effect was also used to draw the viewer's eye to the model's legs in this portrait shown here and make them seem longer. The long, graphic lines of her legs draw the eye up into the centre of the image.
As lenses get more wideangle they have a tendency to distort straight horizontal and vertical lines and turn them into curves - especially those closer to the edges of the frame, or when the camera is tilted. At its most extreme, images take on a spherical perspective and eventually become circular. These are fisheye lenses. Although there is some fun to be had from their novelty value, their real-world uses are quite limited, making them something of a niche purchase.