focus
focus, in optics, the point at which rays converge after reflection by a concave
mirror or refraction by a convex
lens, also known as a real focus. The point from which rays appear to diverge after reflection by a convex mirror or refraction by a concave lens is known as a virtual focus. See
image.
The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
focus
(focal point) See focal length.Collins Dictionary of Astronomy © Market House Books Ltd, 2006
Focus
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
Focus
the area in which a subterranean shock occurs deep in the earth’s crust or in, the upper mantle, resulting in an earthquake.
Focus
in mathematics:
(1) The focus of a curve of degree 2—an ellipse, a hyperbola, or a parabola—is a point F lying in the plane of the curve and possessing the property that the ratio of the distance between any point on the curve and F to the distance to the directrix is a constant equal to the eccentricity.
(2) One of the types of critical points of ordinary differential equations. All integral curves that pass through points in the immediate vicinity of such a critical point are spirals with infinitely many turns that approach the critical point without restriction as they wind around it.
Focus
in optics, the point at which the rays of a parallel beam (or their apparent extension, if the system converts a parallel beam into a divergent beam) intersect after passing through an optical system. If the rays pass parallel to the optical axis of the system, the focus is found on this axis and is called the principal focus. In an ideal optical system, all foci are located on a plane perpendicular to the axis of the system called the focal plane. In a real system, foci are located on some surface called the focal surface.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
focus
[′fō·kəs] (electronics)
To control convergence or divergence of the electron paths within one or more beams, usually by adjusting a voltage or current in a circuit that controls the electric or magnetic fields through which the beams pass, in order to obtain a desired image or a desired current density within the beam.
(geophysics)
The center of an earthquake and the origin of its elastic waves within the earth.
(mathematics)
A point in the plane which together with a line (directrix) defines a conic section.
(nucleonics)
To guide particles along a desired path in a particle accelerator by means of electric or magnetic fields.
(optics)
The point or small region at which rays converge or from which they appear to diverge.
To move an optical lens toward or away from a screen or film to obtain the sharpest possible image of a desired object.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
focus
1. a point of convergence of light or other electromagnetic radiation, particles, sound waves, etc., or a point from which they appear to diverge
3. Optics the state of an optical image when it is distinct and clearly defined or the state of an instrument producing this image
4. Geometry a fixed reference point on the concave side of a conic section, used when defining its eccentricity
5. the point beneath the earth's surface at which an earthquake or underground nuclear explosion originates
6. Pathol the main site of an infection or a localized region of diseased tissue
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
FOCUS
(database, language)A hierarchical
database language from
Information Builders, Inc.
This article is provided by FOLDOC - Free Online Dictionary of Computing (foldoc.org)
FOCUS
(1) (focus) In software, the current window, menu or dialog box that is affected by a key stroke or mouse movement. For example, after you click from one window to another, the second one is said "to have the focus."
(2) (Federation On Computing in the United States, www.acm.org/focus) The U.S. representative of the International Federation for Information Processing (IFIP), www.ifip.or.at. FOCUS was founded in 1991 by the ACM and the IEEE Computer Society (IEEE-CS).
(3) A DBMS from Information Builders that runs on more than 35 different platforms. FOCUS has been widely known for its 4GL and report writing capabilities and is the product that built the company. It included a hierarchical database in its first release in 1975 and has evolved to support more than 80 database and file types including Information Builders' own multidimensional database (FOCUS Fusion). See EDA, WebFOCUS and FOCUS Fusion.Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.
