Wide-angle lens

lens whose focal length is substantially smaller than the focal length of a normal lens for a given film plane

A wide-angle lens is a lens that has a focal length that is shorter than that of the normal lens. Normal lenses have an angle of view of between 40° and 50°. Wide-angle lenses have an angle of view that is bigger.

One of Canon's most popular wide-angle lenses - 17-40 mm f/4 L retrofocus zoom lens.
A wide-angle photograph of steps showing the perspective distortion. The distortion is due to the distance at which the picture is taken. The front stairs appear to tip forward.

For the 135 film format (the most popular photographic film type), normal lenses are 50mm focal length. 35mm (with an angle of view of 63 degrees) and 28mm (75°) are slight wide-angle lenses.

24mm (84°), 20mm (94°), 17mm (104°) and 14mm (114°) offer more extreme views (for 35mm film).

This is different for digital photography. Many digital cameras use smaller sensors. This means that the focal lengths have an angle of view that is smaller. That way, an 18mm lens mounted on a digital camera of this type gives an angle of view of the 28mm wide-angle lens, namely 75 degrees, for a multiplier of 1.5.

One kind of wide-angle lens is a fish eye lens.

Telephoto lens is the opposite. It has a long focal length, and a narrow angle of view.