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focal length |
Also found in: Medical, Wikipedia, Hutchinson | 0.04 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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