Elementary treatise on physics experimental and applied for the use of colleges and schools (1890)
Ganot, A. (Adolphe), 1804-1887, Atkinson, E. (Edmund) · New York : W. Wood · leaf 543
Iig. 501. -552] Foci in Double Convex Lenses. 525 … it can be shown by calculation that they all pass very nearly through thepoint F, so long as the arc DE does not exceed 10° to 12°. This point iscalled the principal focus, and the distance FA is xhe pri?tcipal focal dis-tatice. It is constant in the same lens, but varies with the radii of…
Physics
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