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Zoom lenses are often described by the ratio of their longest to shortest focal lengths. For example, a zoom lens with focal lengths ranging from 100 mm to 400 mm may be described as a 4:1 or "4×" zoom. Typical zoom lenses cover a 3.5× range, for example 24–90 mm (standard zoom) or 60–200 mm (telephoto zoom).
The focal point F and focal length f of a positive (convex) lens, a negative (concave) lens, a concave mirror, and a convex mirror.. The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power.
Optically designed as a reverse telephoto to enable the lens to fit into a standard mount as the focal length can be less than the distance from lens mount to focal plane. Long-focus lens - a lens with a focal length greater than the diagonal of the film frame or sensor. Long focus lenses are relatively simple to design, the challenges being ...
A zoom lens is a system of camera lens elements for which the focal length (and thus angle of view) can be varied, as opposed to a fixed-focal-length (FFL) lens . A true zoom lens or optical zoom lens is a type of parfocal lens , one that maintains focus when its focal length changes. [ 1 ]
Angle of view is narrower. The most common type of long-focus lens is the telephoto lens, a design that uses special optical configurations to make the lens shorter than its focal length. A side effect of using lenses of different focal lengths is the different distances from which a subject can be framed, resulting in a different perspective ...
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. [4]
Minimum focal lengths at the same angle of view (diagonal angle ≈ 107°) Maximum focal lengths at the same angle of view (diagonal angle ≈ 62°) F-number at the same depth of field ISO speed at the same exposure time Nikon CX: 6 mm: 13.5 mm: 2.8: 100 MFT: 8 mm: 18 mm: 4.0: 200: APS-C: 11 mm: 24 mm: 5.6: 360 Full frame: 16 mm: 36 mm: 8.0: 800
Notice that the shorter the focal length and the larger the angle of view, perspective distortion and size differences increase. Lenses are often referred to by terms that express their angle of view: Fisheye lenses, typical focal lengths are between 8 mm and 10 mm for circular images, and 15–16 mm for full-frame images. Up to 180° and beyond.