Photographic optics and colour photography : including the camera, kinematograph, optical lantern, and the theory and practice of image formation / by George Lindsay Johnson.

  • Johnson, G. Lindsay (George Lindsay), 1853-1943.
Date:
1909
Catalogue details

Licence: In copyright

Credit: Photographic optics and colour photography : including the camera, kinematograph, optical lantern, and the theory and practice of image formation / by George Lindsay Johnson. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    Therefore r = <Jd\ [2] and d = ^ [3] In other words, the distance of the pinhole from the plate equals square of the radius of the pinhole, divided by the length of a light wave (0,59^ to 0,4//,). Example.—What is the correct diameter to make the pinhole for a camera 10 in. in length, the object being very remote compared with the length of the camera ? The distance of the plate from the pinhole is 10 in., and X = 0,000016 in., or 0,0004 mm. Therefore r = V0,000016 x 10 = 0,013 in. S S Fig. 2.—Diagram to illustrate the method of calculating the size of the aperture. The correct diameter of the pinhole will therefore be 0,026 in. = ^ in. (nearly) If the object be near compared with the length of the camera, another formula must be used. Let /, be distance of the pinhole from the plate, fx the distance of the object from the pinhole, and d the diameter of the pinhole. Then * = £r? x °-81 m Ji ~rj2 the latter being a constant, gives the value in millimetres, when /j and f2 are expressed in metres or decimals of a metre. Example.—The object is 2 metres distant, and the plate 0,25 metre (10 in.) from the pinhole: what will be the most effective aperture ? Here fx = 2,/2 = 0,25, mu c n °>25 x 2 x 0,81 niQ Therefore d2 = ^ '— = 0,18 and d = ^0718 = 0,42 mm.