Definition of focus

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Focus (n.) A point so related to a conic section and certain straight line called the directrix that the ratio of the distace between any point of the curve and the focus to the distance of the same point from the directrix is constant.

Lern More About Focus

Focus :: Focus (n.) A point in which the rays of light meet, after being reflected or refrcted, and at which the image is formed; as, the focus of a lens or mirror..
Sunglow :: Sunglass (n.) A convex lens of glass for producing heat by converging the sun's rays into a focus.
Image :: Image (n.) The figure or picture of any object formed at the focus of a lens or mirror, by rays of light from the several points of the object symmetrically refracted or reflected to corresponding points in such focus; this may be received on a screen, a photographic plate, or the retina of the eye, and viewed directly by the eye, or with an eyeglass, as in the telescope and microscope; the likeness of an object formed by reflection; as, to see one's image in a mirror..
Focal :: Focal (a.) Belonging to,or concerning, a focus; as, a focal point..
Eccentricity :: Eccentricity (n.) The ratio of the distance between the center and the focus of an ellipse or hyperbola to its semi-transverse axis.
Micrometer :: Micrometer (n.) An instrument, used with a telescope or microscope, for measuring minute distances, or the apparent diameters of objects which subtend minute angles. The measurement given directly is that of the image of the object formed at the focus of the object glass..
Hypermetropy :: Hypermetropy (n.) A condition of the eye in which, through shortness of the eyeball or fault of the refractive media, the rays of light come to a focus behind the retina; farsightedness; -- called also hyperopia. Cf. Emmetropia..
Hyperbola :: Hyperbola (n.) A curve formed by a section of a cone, when the cutting plane makes a greater angle with the base than the side of the cone makes. It is a plane curve such that the difference of the distances from any point of it to two fixed points, called foci, is equal to a given distance. See Focus. If the cutting plane be produced so as to cut the opposite cone, another curve will be formed, which is also an hyperbola. Both curves are regarded as branches of the same hyperbola. See Illust. o
Directrix :: Directrix (n.) A straight line so situated with respect to a conic section that the distance of any point of the curve from it has a constant ratio to the distance of the same point from the focus.
Focus :: Focus (v. t.) To bring to a focus; to focalize; as, to focus a camera..
Convergent :: Convergent (a.) tending to one point of focus; tending to approach each other; converging.
Focuses :: Focuses (pl. ) of Focu.
Aberration :: Aberration (n.) The convergence to different foci, by a lens or mirror, of rays of light emanating from one and the same point, or the deviation of such rays from a single focus; called spherical aberration, when due to the spherical form of the lens or mirror, such form giving different foci for central and marginal rays; and chromatic aberration, when due to different refrangibilities of the colored rays of the spectrum, those of each color having a distinct focus..
Parabola :: Parabola (n.) A kind of curve; one of the conic sections formed by the intersection of the surface of a cone with a plane parallel to one of its sides. It is a curve, any point of which is equally distant from a fixed point, called the focus, and a fixed straight line, called the directrix. See Focus..
Focalize :: Focalize (v. t.) To bring to a focus; to focus; to concentrate.
Focusing :: Focusing (p. pr. & vb. n.) of Focu.
Diaphragm :: Diaphragm (n.) A plate with an opening, which is generally circular, used in instruments to cut off marginal portions of a beam of light, as at the focus of a telescope..
Collimator :: Collimator (n.) A tube having a convex lens at one end and at the other a small opening or slit which is at the principal focus of the lens, used for producing a beam of parallel rays; also, a lens so used..
Emmetropia :: Emmetropia (n.) That refractive condition of the eye in which the rays of light are all brought accurately and without undue effort to a focus upon the retina; -- opposed to hypermetropia, myopia, an astigmatism..
Ellipse :: Ellipse (n.) An oval or oblong figure, bounded by a regular curve, which corresponds to an oblique projection of a circle, or an oblique section of a cone through its opposite sides. The greatest diameter of the ellipse is the major axis, and the least diameter is the minor axis. See Conic section, under Conic, and cf. Focus..
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