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Eng ID Term Definition
1881
focal distance
See FOCAL LENGTH.
1882
focal length
The distance from the rear NODAL POINT of a LENS to the FOCAL PLANE for an object at infinity. The distance from the surface of a MIRROR to ... more
The distance from the rear NODAL POINT of a LENS to the FOCAL PLANE for an object at infinity. The distance from the surface of a MIRROR to its FOCUS. Also called focal distance.
1883
focal length: calibrated
An adjusted value of the EQUIVALENT FOCAL LENGTH computed to distribute the effect of lens DISTORTION over the entire field used in an AERIA... more
An adjusted value of the EQUIVALENT FOCAL LENGTH computed to distribute the effect of lens DISTORTION over the entire field used in an AERIAL CAMERA.
1884
focal length: equivalent
The distance measured along the AXIS OF LENS from the rear NODAL POINT to the plane of best average DEFINITION over the entire field used in... more
The distance measured along the AXIS OF LENS from the rear NODAL POINT to the plane of best average DEFINITION over the entire field used in an AERIAL CAMERA.
1885
focal plane
A plane parallel to the plane of a LENS or MIRROR and passing through the FOCUS. In PHOTOGRA­PHY, the plane (perpendicular to the axis of t... more
A plane parallel to the plane of a LENS or MIRROR and passing through the FOCUS. In PHOTOGRA­PHY, the plane (perpendicular to the axis of the LENS) in which IMAGES of points in the object field of the LENS are focused.
1886
focal-plane plate
A glass plate set in the CAMERA so that the surface away from the LENS coincides with the FOCAL PLANE. Its purpose is to position the EMULSI... more
A glass plate set in the CAMERA so that the surface away from the LENS coincides with the FOCAL PLANE. Its purpose is to position the EMULSION of the film in the FOCAL PLANE when the film is physically pressed into contact with the glass plate. Also called contact glass or contact plate.
1887
focal-plane shutter
See SHUTTER.
1888
focal point
See FOCUS.
1889
focus
(pl. foci). That point at which parallel RAYS of light meet after being refracted by a LENS or reflected by a MIRROR. Also called focal poin... more
(pl. foci). That point at which parallel RAYS of light meet after being refracted by a LENS or reflected by a MIRROR. Also called focal point. In SEISMOLOGY, the source of a given set of elastic WAVES. The true centre of an EARTHQUAKE, within which the strain energy is first converted to elastic wave energy.
1890
focus
(v.t.). The process of adjusting an optical instrument, PROJECTOR, CATHODE-RAY TUBE, etc., to produce a clear and well-defined IMAGE.
1891
fog
Suspension of very small water droplets in the air, generally reducing the horizontal VISIBILITY at the EARTH's surface to less than 1 kilom... more
Suspension of very small water droplets in the air, generally reducing the horizontal VISIBILITY at the EARTH's surface to less than 1 kilometre.
1892
fog: advection
FOG which forms in the lower part of a moist AIR MASS which moves over a colder surface.
1893
fog: ice
Suspension of numerous minute ice crystals in the air, reducing the VISIBILITY at the EARTH's sur­face.
1894
fog: sea
ADVECTION FOG which forms over the SEA.
1895
fog: wet
FOG formed of droplets sufficiently large to deposit water on objects.
1896
fog bank
FOG, generally caused by local conditions, which extends over a small area some hundreds of METRES wide.
1897
fog bell
A bell used as a FOG SIGNAL.
1898
fog detector light
A light used to automatically determine conditions of visibility which warrant the turning on or off of a sound signal.
1899
fog gong
A gong used as a FOG SIGNAL.
1900
fog gun
A gun used as a FOG SIGNAL.