It is important to distinguish the angle of view from the angle of coverage, which describes the angle range that a lens can image.Typically the image circle produced by a lens is large enough to cover the film or sensor completely, possibly including some vignetting toward the edge.If the angle of coverage of the lens does not fill the sensor, the image circle will be visible, typically with strong vignetting toward the edge, and the effective angle of view will be limited to the angle of coverage.
Examples:
An example of how lens choice affects angle of view.The photos below were taken by a 35 mm still camera at a constant distance from the subject:
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| 50 mm lens |
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| 70 mm lens |
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| 210 mm lens |
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| 28 mm lens |
In photography a wide-angle lens refers
to a lens whose focal length is substantially smaller than the focal length 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, or a wide field of view.
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 lens
of roughly twice the diagonal is considered "normal".
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 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 backwards 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.
http://en.wikipedia.org/wiki/Wide-angle_lens
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