Lummer, O. (Otto), 1860-1925, Thompson, Silvanus P. (Silvanus Phillips), 1851-1916 · London, New York, Macmillan and Co., 1900 · leaf 75
goal. At the time photography came into existence, when Draper of Xew York obtained, in 1840, the first portrait of a living person with an exposure of two to twenty minutes duration, it was the keen desire of all concerned to possess an objective which transmitted more light, such as would shorten… … making photography IS.-Pet.val'.s Portrait-Objective. popular. In this ob- jective, depicted in Pig. 13, everything else was sacrificed to the aim of obtaining, with a great aperture-ratio of almost //3,
Photographic optics
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