Focal Length

The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus. A system with a shorter focal length has greater optical power than one with a long focal length; that is, it bends the rays more strongly, bringing them to a focus in a shorter distance.

In most photography and all telescopy, where the subject is essentially infinitely far away, longer focal length (lower optical power) leads to higher magnification and a narrower angle of view; conversely, shorter focal length or higher optical power is associated with a wider angle of view. On the other hand, in applications such as microscopy in which magnification is achieved by bringing the object close to the lens, a shorter focal length (higher optical power) leads to higher magnification because the subject can be brought closer to the center of projection.

Read more about Focal Length:  Thin Lens Approximation, General Optical Systems, In Photography

Other articles related to "focal length, focal lengths, focal":

Focal Length - In Photography
... Camera lens focal lengths are usually specified in millimetres (mm), but some older lenses are marked in centimetres (cm) or inches ... Focal length (f) and field of view (FOV) of a lens are inversely proportional ... separated from the sensor or film, at the focal plane, by the lens's focal length ...
Canon EF 85mm Lens
... that share the same focal length ... This 85mm focal length is perfect for portraiture as labeled by Canon and practicing professionals, due to the focal length creating just the right perspective for both the subject and the background ... a 70-200mm for complementing the longer focal lengths, usually for shooting full body portraiture ...
Clarke Observatory - Observatories
... Saegmuller 9-inch refractor, 117-inch focal length First Light 1897? Dome Material bronze Directors Charles Ezra Hequembourg, private owner (1897-1907) Mrs ... Saegmuller 9-inch refractor, 117-inch focal length, moved from New York Directors Elmer Harrold, private owner (1917-1919), donated to Mount Union College Third Observatory Location Alliance, Ohio Construction Began ...
Senior Portraits - Lenses
... narrow field of view of 30 degrees, a focal length of 150mm, and a fast f-number in the f/3.3-3.7 range ... Classic focal length is in the range 80–135mm on 135 film format and about 150-400mm on large format, which historically is first in photography ... Wider angle lenses (shorter focal length) require that the portrait be taken from closer (for an equivalent field size), and the resulting perspective distortion yields a ...
Convex Mirror - Analysis - Mirror Equation and Magnification
... as the mirror and lens equation, relates the object distance and image distance to the focal length ... The sign convention used here is that the focal length is positive for concave mirrors and negative for convex ones, and and are positive when the ... or real depends on how large the object distance is compared to the focal length ...

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