Photographic optics and colour photography [electronic resource] : including the camera, kinematograph, optical lantern, and the theory and practice of image formation (1909)
Johnson, G. Lindsay (George Lindsay), 1853-, Parsons, John Herbert, Sir, 1868-1957, donor, University College, London. Library Services · London : Ward & Co. · leaf 101
d by the formula [22] tan u' Lastly, the focal length may be denned as that distance measured along the optic axis through which the object must be moved to produce an increase or decrease of one magnification in the image (Blakesley's definition). The knowledge of the precise focal length of a… … Fig. 62. — Diagram showing how the focal length is obtained. this point be readily found unless the true focal distance is known, so that we must either adopt other means to find the points from which to take our measure, or else the focal length must be found independently. The true focal length…
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