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focal length |
Also found in: Medical, Acronyms, Wikipedia, Hutchinson | 0.07 sec. |
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focal length, distance the distance from the focal point of a lens or mirror to the reflecting surface of the mirror or the centre point of the lens Focal length A measure of the collecting or diverging power of a lens or an optical system. Focal length, usually designated f ′ in formulas, is measured by the distance of the focal point (the point where the image of a parallel entering bundle of light rays is formed) from the lens, or more exactly by the distance from the principal point to the focal point. See Geometrical optics The power of a lens system is equal to n′/f ′, where n′ is the refractive index in the image space (n′ is usually equal to unity). A lens of zero power is said to be afocal. Telescopes are afocal lens systems. See Diopter, Lens (optics), Telescope How to thank TFD for its existence? Tell a friend about us, add a link to this page, add the site to iGoogle, or visit webmaster's page for free fun content. |
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| That makes an effective focal length of 840mm - `the same effect as using binoculars," Davies says. The system is fully motorised with microprocessor control, and the lens offers parfocal selection of five effective focal lengths, four selectable filters and a four-line backlit display of focal length, filter position, focus range and operating status. 5-mm2 with a diagonal dimension of 28-mm, resulting in an effective focal length multiplier of 1. |
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