focal planen.
/ˈfəʊkl pleɪn/, U.S. /ˈfoʊk(ə)l pleɪn/ Optics.
A plane in which initially parallel rays come to a focus after refraction by a lens or lens system or reflection by a curved mirror, and in which (in the case of visible light) images of distant objects are formed. Frequently attributive. Cf. focal surface n. (b) at focal adj. Compounds.
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1840 Civil Engineer & Architect's Jrnl. 3 385/2 ‘Daguerreotype’..is the art of fixing and preserving on the surface of a polished silvered plate the images collected in the focal plane of a camera obscura.
1895 R. S. Heath Geom. Optics (ed. 2) 82 An incident system of parallel rays will then converge to a point on the common focal plane.
1906 Westm. Gaz. 8 Sept. 14/2 In a piece of apparatus so complex as the focal-plane reflecting camera.
1921 H. G. Ponting Great White South 58 To make focal-plane photographic exposures.
1990 A. Boyde in J. B. Pawley Handbk. Biol. Confocal Microsc. (rev. ed.) xv. 164/1 In order to obtain three-dimensional information, it is necessary to examine sets of two-dimensional images corresponding to different focal planes.
2011 Optician 15 Apr. 34/1 HST [= Hubble Space Telescope] is designed to house several instruments that can be moved individually into the focal plane of the mirror system.
Compounds
focal plane array n. an apparatus consisting of an array of sensors or receivers located at the focal plane of a focusing device, typically allowing imaging or sensing of a given area without the need for scanning.
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1962 IRE Trans. Nucl. Sci. 9 149/2 The lower part of Fig. 26 shows a photograph of..a Po210 alpha test source centered opposite the focal plane array.
1986 Pop. Sci. July 16/3 Northrop's focal plane array is an experimental semiconductor chip that ‘sees’ by detecting the amount of infrared light..radiated from an object.
2010 Seeing Photons (National Acad. Sci.–National Res. Council (U.S.)) ii. 57 A focal plane array is created by arranging individual detector elements in a lattice-like array.
focal-plane shutter n. Photography a camera shutter which is located immediately in front of the focal plane, and which operates by passing a slit across the photographic plate or film.Because it exposes only a small portion of the plate or film at a time, a focal-plane shutter effectively allows faster speeds at a given relative aperture than a between-lens shutter.
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1885 Photogr. News 27 Nov. 767/2 Barker's focal plane shutter has a great advantage over other exposers.
1905 Westm. Gaz. 21 Oct. 18/2 In photographing rapidly moving objects the focal-plane shutter does give unmistakable distortion.
1950 G. L. Wakefield Your Camera Lens & Shutter 86 A between-lens shutter exposes the whole of the film at once; the focal-plane shutter..exposes it piecemeal in strips.
2008 PTN Nov. 20/3 Why not build leaf shutters into them, in addition to the customary focal-plane shutter of DSLRs?
This entry has been updated (OED Third Edition, September 2016; most recently modified version published online March 2022).
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