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CONVEX

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Originally appearing in Volume V23, Page 4 of the 1911 Encyclopedia Britannica.
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CONVEX See also:

MIRROR Position of See also:Object. Position of See also:Image. See also:Character of Image. to Between co and A A The above discussion of spherical mirrors assumes that the mirror has such a small See also:aperture that the reflected rays from any point unite in a point. This, however, no longer holds when the mirror has a wide aperture, and in See also:general the reflected rays envelop a See also:caustic (q.v., see also See also:ABERRATION). The only mirror which can sharply reproduce an object-point as an image-point has for its See also:section an See also:ellipse, which is so placed that the object and image are at its foci. This follows from a See also:property of the See also:curve, viz. the sum of the See also:focal distances is See also:constant, and that the focal vectores are equally inclined to the normal at the point. More important than the elliptical mirror, however, is the parabolic, which has the property of converting rays parallel to,the See also:axis into a See also:pencil through its See also:focus; or, inversely, rays from a source placed at the focus are converted into a parallel See also:beam; hence the use of this mirror in See also:search-See also:lights and similar devices.

End of Article: CONVEX

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