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: Public Domain Mark

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.

    22/354 (page 2)
    of the pinhole. If the hole be very large compared to a wave length, the number of waves retarded is insignificant compared with the mass of unimpeded waves, and the diffraction will be unnoticeable; but if the hole be small compared with a wave length, the image which would otherwise be formed clearly and sharply, as if drawn with a pencil point equal in size to the pinhole, is impaired by the diffraction images. This is why a special hole must be found which will give the best results for a given distance of object and image. The method of calculation is usually made on my Ray- _ leigh’s supposition that the limit of retardation should be taken Fie. 1.—Diagram showing the path of rays in a pinhole camera. . AB is the object ; BA the image (reversed). a8 5; A being the wave length for ordinary photographie blue- bi light. A ‘ ‘ Let 5 be the retardation (Fig. 2); ry the radius of pinhole aq’ ; and d the distance from the plate 8; also let aa’ be perpendicular to a'P, the axis. Then, if dP =d,aP=ad+5 Since the angle aa'P is a right angle } A\? r? + (P= (4 an 3) . (Huclid I. 47.) i} Therefore ‘bs =(4+5) <r =@+a4> — d*= dr : wis since 7 » being very small, may be neglected.