In photography, a long-focus lens is a camera lens which has a focal length that is longer than the diagonal measure of the film or sensor that receives its image.
It is used to make distant objects appear magnified with magnification increasing as longer focal length lenses are used. A long-focus lens is one of three basic photographic lens types classified by relative focal length, the other two being a normal lens and a wide-angle lens.
As with other types of camera lenses, the focal length is usually expressed in a millimeter value written on the lens, for example: a 500 mm lens. The most common type of long-focus lens is the telephoto lens, which incorporate a special lens group known as a telephoto group to make the physical length of the lens shorter than the focal length.
Long-focus lenses are best known for making distant objects appear magnified. This effect is similar to moving closer to the object, but is not the same, since perspective is a function solely of viewing location. Two images taken from the same location, one with a wide angle lens and the other with a long-focus lens, will show identical perspective, in that near and far objects appear the same relative size to each other. Comparing magnification by using a long lens to magnification by moving closer, however, the long-focus-lens shot appears to compress the distance between objects due to the perspective from the more distant location. Long lenses thus give a photographer an alternative to the type of perspective distortion exhibited by shorter focal length lenses where (when the photographer stands closer to the given subject) different portions of a subject in a photograph can appear out of proportion to each other.
Long lenses also make it easier to blur the background more, even when the depth of field is the same; photographers will sometimes use this effect to defocus the background in an image to "separate" it from the subject. This background blurring is often referred to as bokeh by photographers.
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Ce cours d'introduction à la microscopie a pour but de donner un apperçu des différentes techniques d'analyse de la microstructure et de la composition des matériaux, en particulier celles liées aux m
The course deals with the concept of measuring in different domains, particularly in the electrical, optical, and microscale domains. The course will end with a perspective on quantum measurements, wh
A telephoto lens, in photography and cinematography, is a specific type of a long-focus lens in which the physical length of the lens is shorter than the focal length. This is achieved by incorporating a special lens group known as a telephoto group that extends the light path to create a long-focus lens in a much shorter overall design. The angle of view and other effects of long-focus lenses are the same for telephoto lenses of the same specified focal length.
In photography and cinematography, 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.
In photography and cinematography, a normal lens is a lens that reproduces a field of view that appears "natural" to a human observer. In contrast, depth compression and expansion with shorter or longer focal lengths introduces noticeable, and sometimes disturbing, distortion. Photographic technology employs different physical methods from the human eye in order to capture images. Thus, manufacturing optics which produce images that appear natural to human vision is problematic.
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