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The focal length of a Wide Angle Lens is considerably shorter than the focal
length of a regular lens for the image size produced by the respective camera.
In other words, with wide angle lenses, you can capture depth in a shot. You are
simply broadening the angle of view A wide-angle photograph of steps showing the perspective distortion due to the distance at which the
picture is taken. The front stairs appear to tip forward. .In
photography and cinematography, a wide-angle lens is a lens whose focal length is substantially shorter than the focal length of a
normal lens for the image size produced by the camera, whether this is dictated by the dimensions of the
image frame at the
film plane for film cameras (film format) or dimensions of the photo
sensor for digital cameras.
One of Canon's most popular wide-angle lenses - 17-40 mm f/4 L retrofocus zoom lens.
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 photo sensor. In cinematography, a somewhat longer lens is considered "normal".
There is an easy formula for calculating the angle of view for any lens that produces a rectilinear image. In addition to giving a wider
angle of view, the image produced by a wide-angle lens is more susceptible to
perspective distortion than that produced by a
normal lens, because they tend to be used much closer to the subject.
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.
For an APS-C Sensor camera this number is reduced to 23mm because of the "crop
factor".
Common wide-angle lenses for a full-frame 35 mm camera are 35, 28, 24, 21, 18 and 14 mm. 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 here).
Extreme wide-angle lenses that do not produce a rectilinear image are called
fisheye lenses. Common focal lengths for these in a 35 mm
camera are 6 to 8 mm (which produce a circular image). Lenses with focal lengths of 14 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 12 mm, including zoom lenses with ranges of 2:1 that also begin at 12 mm. .
Ultra Wide Angle Lens
An ultra wide-angle lens is a lens whose focal length is shorter than the short side of film or sensor.
Digital camera considerations
Apparent focal length in APS-sized digital cameras is increased by a
crop factor. As of 2009, most interchangeable-lens digital cameras have photo sensors that are smaller than the
film format of full-frame 35 mm cameras. For the most part, the dimensions of these photo 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 Sigma DSLRs) and 2 (the
Four-thirds-format 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. As examples, a 28 mm lens would produce on the DSLR (given a crop factor of 1.5) has 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 Best Prices for 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 to this problem 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.
Construction
 Cross-section of a typical short-focus wide-angle lens.
Cross-section of a typical retrofocus wide-angle lens. There are two different varieties of wide-angle lens: short-focus lenses and retrofocus lenses.
Short-focus lenses are generally made up of multiple glass elements whose shapes are more or less symmetrical in front of and behind the diaphragm. As the focal length decreases, the distance of the rear element of the lens from the film plane or digital sensor also decreases. This makes short-focus wide-angle lenses undesirable for
single-lens reflex cameras unless they are used with the reflex mirrors locked up. Short-focus lenses are widely used on
large format
view cameras.
The retrofocus lens solves this proximity problem through an asymmetrical design that allows the rear element to be further away from the film plane than its effective focal length would suggest. (See Angenieux retrofocus.) For example, it is not uncommon for the rear element of a retrofocus lens of 18 mm to be more than 25 mm from the film plane. This makes it possible to design wide-angle lenses for
single-lens reflex cameras.
See also
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