In photography and cinematography, a wide-angle lens is a lens covering a large angle of view. Conversely, its focal length is substantially smaller than that of a normal lens for a given film plane. This type of lens allows more of the scene to be included in the photograph, which is useful in architectural, interior, and landscape photography where the photographer may not be able to move farther from the scene to photograph it. Another use is where the photographer wishes to emphasize the difference in size or distance between objects in the foreground and the background; nearby objects appear very large and objects at a moderate distance appear small and far away. This exaggeration of relative size can be used to make foreground objects more prominent and striking, while capturing expansive backgrounds. A wide-angle lens is also one that projects a substantially larger image circle than would be typical for a standard design lens of the same focal length. This large image circle enables either large tilt & shift movements with a view camera. By convention, in still photography, the normal lens for a particular format has a focal length approximately equal to the length of the diagonal of the image frame or digital photosensor. In cinematography, a lens of roughly twice the diagonal is considered "normal".
Characteristics Longer lenses magnify the subject more, apparently compressing distance and (when focused on the foreground) blurring the background because of their shallower depth of field. Wider lenses tend to magnify the distance between objects while allowing greater depth of field. Another result of using a wide-angle lens is a greater apparent perspective distortion when the camera is not aligned perpendicularly to the subject: parallel lines converge at the same rate as with a normal lens but converge more due to the wider total field. For example, buildings appear to be falling backward much more severely when the camera is pointed upward from ground level than they would if photographed with a normal lens at the same distance from the subject because more of the subject building is visible in the wide-angle shot. Because different lenses generally require a different camera–subject distance to preserve the size of a subject, changing the angle of view can indirectly distort perspective, changing the apparent relative size of the subject and foreground.
Wide-angle lenses for 35 mm format For a full-frame 35 mm camera with a 36 mm by 24 mm format, the diagonal measures 43.3 mm, and by custom, the normal lens adopted by most manufacturers is 50 mm. Also by custom, a lens of focal length 35 mm or less is considered wide-angle. Ultra wide angle lenses have a focal length shorter than the short side of the film or sensor. In 35 mm, an ultra wide-angle lens has a focal length shorter than 24 mm. Common wide-angle lenses for a full-frame 35 mm camera are 35, 28, 24, 21, 20, 18, and 14 mm, the latter four being ultra-wide. Many of the lenses in this range will produce a more or less rectilinear image at the film plane, though some degree of barrel distortion is not uncommon. Ultra wide-angle lenses that do not produce a rectilinear image (i.e., exhibit barrel distortion) are called fisheye lenses. Common focal lengths for these in a 35 mm camera is 6 to 8 mm (which produce a circular image). Lenses with focal lengths of 8 to 16 mm may be either rectilinear or fisheye designs. Wide-angle lenses come in both fixed-focal-length and zoom varieties. For 35 mm cameras, lenses producing rectilinear images can be found at focal lengths as short as 8 mm, including zoom lenses with ranges of 2:1 that begin at 12 mm.
Digital camera considerations
As of 2015, many interchangeable-lens digital cameras have image sensors that are smaller than the film format of full-frame 35 mm cameras. For the most part, the dimensions of these image sensors are similar to the APS-C image frame size, i.e., approximately 24 mm x 16 mm. Therefore, the angle of view for any given focal-length lens will be narrower than it would be in a full-frame camera because the smaller sensor "sees" less of the image projected by the lens. The camera manufacturers provide a crop factor (sometimes called a field-of-view factor or a focal-length multiplier) to show how much smaller the sensor is than a full 35 mm film frame. For example, one common factor is 1.5 (Nikon DX format and some others), although many cameras have crop factors of 1.6 (most Canon DSLRs), 1.7 (the early Sigma DSLRs) and 2 (the Four Thirds and Micro Four Thirds cameras). The 1.5 indicates that the angle of view of a lens on the camera is the same as that of a 1.5 times longer focal length on a 35 mm full-frame camera, which explains why the crop factor is also known as a focal-length multiplier. For example, a 28 mm lens on the DSLR (given a crop factor of 1.5) would produce the angle of view of a 42 mm lens on a full-frame camera. So, to determine the focal length of a lens for a digital camera that will give the equivalent angle of view as one on a full-frame camera, the full-frame lens focal length must be divided by the crop factor. For example, to get the equivalent angle of view of a 30 mm lens on a full-frame 35 mm camera, from a digital camera with a 1.5 crop factor, one would use a 20 mm lens. Lens manufacturers have responded by making wide-angle lenses of much shorter focal lengths for these cameras. In doing this, they limit the diameter of the image projected to slightly more than the diagonal measurement of the photosensor. This gives the designers more flexibility in providing the optical corrections necessary to economically produce high-quality images at these short focal lengths, especially when the lenses are zoom lenses. Examples are 10 mm minimum focal length zoom lenses from several manufacturers. At 10 mm, these lenses provide the angle of view of a 15 mm lens on a full-frame camera when the crop factor is 1.5.
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