# focus

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## focus,

in optics, the point at which rays converge after reflection by a concave mirrormirror,
in optics, a reflecting surface that forms an image of an object when light rays coming from that object fall upon it (see reflection). Usually mirrors are made of plate glass, one side of which is coated with metal or some special preparation to serve as a reflecting
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or refraction by a convex lenslens,
device for forming an image of an object by the refraction of light. In its simplest form it is a disk of transparent substance, commonly glass, with its two surfaces curved or with one surface plane and the other curved.
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, 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 imageimage,
in optics, likeness or counterpart of an object produced when rays of light coming from that object are reflected from a mirror or are refracted by a lens. An image of an object is also formed when this light passes through a very small opening like that of a pinhole
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.

## focus

(focal point) See focal length.

## Focus

A center of interest or activity drawing attention to the most important aspect of a design scheme, such as the main space, materials, scale, lighting, or orientation.

## 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.

## 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.

## 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
2. another name for focal point focal length
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

## FOCUS

(database, language)
A hierarchical database language from Information Builders, Inc.

## FOCUS

(1) 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.

(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) (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."
References in periodicals archive ?
As Doherty (this issue) shows, also English topicalization requires the focus position to be filled by something focusable.
Infiniprobe UV video microscopes feature a continuously focusable design and easily mount to video cameras.
The X2 Sub Compact includes a Slide Lock interface, focusable beam and intuitive rocker switch with constant on and momentary settings.
The product features a focusable lamp, up to 14 hours of standard usage, an environmentally friendly battery, as well as external programming capability for frequency change and minor maintenance.
Features of which included a BDC calibrated to 800 or 1,200 meters, large objective lens, a focusable ocular lens, and, for the time period, superb light transmission and resolving power.
Its optics proved excellent, with sharp stars across most of the field and a focusable front objective.
While lexical elements, like only, assign focus to constituents in their scope or express inherently focused concepts, like for example superlatives, syntactic structures assign focus in certain grammatical configurations, for example to a verb-adjacent focusable element in the verb phrase (see Jacobs 1988: Rosengren 1991 Abraham 1992; etc.
Ortek's Type 5157 night vision goggles use two focusable 26.
25 Abbe condenser with filter holder , Rack & Pinion focusable Focusing : Coaxial Coarse and Fine controls, 15mm stroke, Coarse: 32mm/turn, Fine: 0.
A combination of focusable and fixed focus LED technology providing quality illumination that is bright, cool and shadow-free for every procedure.
This lens is focusable from 50 mm to infinity and features a fixed F/8 aperture that allows for a balance between depth of field and resolution while maintaining significant light-gathering power.

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