Carpenter, William Benjamin, 1813-1885, Dallinger, W. H. (William Henry), 1842-1909 · Philadelphia, Blakiston · leaf 39
Fig. 15.—Rays diverge when a radiant is placed between a lens and itsprincipal focus. Focus of divergent rays is virtual. meet in a point. This is called the virtual conjugate focus of theradiant. The principal focus of a concave (or diverging) lens isshown in fig. 16. It will be seen that the… … Fig. 16.—Virtual focus of concave lens. divergent on the other side of the lens, and consequently can nevercome to a focus. But if we trace these divergent rays backwards,as in the dotted lines of fig. 16, we find that they meet in a point,and this point is called the virtual principal focus of the…
Microscopy
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