Elementary natural philosophy : designed for high schools and academies (1881)
Griffin, La Roy F. (La Roy Freese), 1844-1916 · Philadelphia : Sower, Potts & Co. · leaf 215
Fig. 237. 711. Images by Concave Lenses. If an object be placed in frontof a double concave lens, therays will be divergent after re-fraction. The required pointsare found by drawing the axes,AO and BO, Fig. 237, and trac-ing rays until they meet theseaxes. Then the point A isfound at a, and B at… … Hence the image is diminished, is direct, and is virtual. 712. Aberration. Spherical mirrors and lenses must besmall, not exceeding 10° or 12°, else the external rays willcome to a focus before those near the middle. This pre-vents a sharply defined focus, lengthening it in the direc-tion of the…
Physics
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