Lummer, O. (Otto), 1860-1925, Thompson, Silvanus P. (Silvanus Phillips), 1851-1916 · London, New York, Macmillan and Co., 1900 · leaf 98
image. This depends upon finding suitable sorts of glass. In the modified lens-system, either one lens or the other, or both, is made up of a cemented pair chosen so that both the kinds of glass used have the same, or nearly the same, mean refractive index, while possessing very different… … Fig. 28. — Planar Objective a sufficiently large selection of of Zeiss. .glasses from which to select those suited for the jiurpose. A slight departure from exact agree- ment in the mean refractivity is quite admissible, and indeed
Photographic optics
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