relative aperture


relative aperture
the ratio of the diameter of a lens, esp. a camera lens, to the focal length; the reciprocal of the f number or focal ratio of the lens.

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optics
      the measure of the light-gathering power of an optical system. It is expressed in different ways according to the instrument involved. The relative aperture for a microscope is called the numerical aperture (NA) and is equal to the sine of half the angle subtended by the aperture at an object point times the index of refraction of the medium between the object and the objective lens. For binoculars, telescopes, and photographic lenses in which the object may be distant, the relative aperture is taken as the ratio of focal length of the objective to the diameter of the entrance pupil. The relative aperture of a camera lens is sometimes expressed as a simple ratio—e.g., 1:4.5—or more commonly as its f-number, f/4.5. In either case, a lens of 180-millimetre focal length set at this relative aperture would have a pupil diameter (effectively, the lens diaphragm opening) of 40 mm.

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Universalium. 2010.

Look at other dictionaries:

  • relative aperture — noun : a measure of the angle of the cone of light rays from an object that traverse an optical system; specifically : the effective aperture of a camera lens expressed as a fraction of its focal length with the symbol f being used instead of 1… …   Useful english dictionary

  • relative aperture — santykinė apertūra statusas T sritis fizika atitikmenys: angl. aperture ratio; relative aperture vok. Öffnungsverhältnis, n; relative Apertur, f rus. относительная апертура, f pranc. ouverture relative, f …   Fizikos terminų žodynas

  • Lens [object(ive) glass, relative] aperture — Относительное отверстие объектива …   Краткий толковый словарь по полиграфии

  • aperture ratio — santykinė apertūra statusas T sritis fizika atitikmenys: angl. aperture ratio; relative aperture vok. Öffnungsverhältnis, n; relative Apertur, f rus. относительная апертура, f pranc. ouverture relative, f …   Fizikos terminų žodynas

  • aperture — apertural /ap euhr choor euhl/, adj. apertured, adj. /ap euhr cheuhr/, n. 1. an opening, as a hole, slit, crack, gap, etc. 2. Also called aperture stop. Optics. an opening, usually circular, that limits the quantity of light that can enter an… …   Universalium

  • relative Apertur — santykinė apertūra statusas T sritis fizika atitikmenys: angl. aperture ratio; relative aperture vok. Öffnungsverhältnis, n; relative Apertur, f rus. относительная апертура, f pranc. ouverture relative, f …   Fizikos terminų žodynas

  • aperture ratio — noun : relative aperture * * * Optics. See relative aperture. [1885 90] …   Useful english dictionary

  • aperture ratio — Optics. See relative aperture. [1885 90] * * * …   Universalium

  • Aperture — For other uses, see Aperture (disambiguation). f stops demonstrated on a lens …   Wikipedia

  • ouverture relative — santykinė apertūra statusas T sritis fizika atitikmenys: angl. aperture ratio; relative aperture vok. Öffnungsverhältnis, n; relative Apertur, f rus. относительная апертура, f pranc. ouverture relative, f …   Fizikos terminų žodynas


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