Lummer, O. (Otto), 1860-1925, Thompson, Silvanus P. (Silvanus Phillips), 1851-1916 · London, New York, Macmillan and Co., 1900 · leaf 139
second element. If one applies the equation of Clausius to the formation of the image of an element of surface hy means of ivide-angled pencils of rays traversing an optical system, one obtains the sine-condition, and for its constant the same value as Abbe and von Helmholtz have assigned to it.… … QB of the object PA by means of suitably wide-angled pencils, the “optical lengths”^ between the conjugate pairs of points are in every possible way equal to one another, apart in this case also from small differences of a negligibly small order of magnitude. Hockin’s process consists in taking…
Photographic optics
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