Wide-angle lens
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.
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.
Wide-angle Lens Media
How focal length affects photograph composition. Three images depict the same two objects, kept in the same positions. By changing the focal length and adjusting the camera's distance from the pink bottle, it remains the same size in the image, while the blue bottle's size appears to dramatically change. Also note that at small focal lengths, more of the scene is included.
Field of view in APS-sized digital cameras is the same as that of a longer lens, increased by crop factor, on a full-frame 35 mm format camera.
Cross-section of a typical short-focus wide-angle lens.
Cross-section of a typical retrofocus wide-angle lens.
Effective focal length is measured from the sensor to where the light cone going to the sensor is the same size as the lens front opening.
