focus(redirected from virtual 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
..... Click the link for more information. 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.
..... Click the link for more information. , 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
..... Click the link for more information. .
focus(focal point) See focal length.
the area in which a subterranean shock occurs deep in the earth’s crust or in, the upper mantle, resulting in an earthquake.
(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.
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(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.