Hawkins Electrical Guide

Hawkins Electrical Guide

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1922 edition. Excerpt: ...of a tea cup or a glass tumbler, a section of the caustic surface can be sem by partly fillinf the cup or tumbler: with _milk. Spherical aberration may be avoided by the use of a parabo ic mirror. The pomt C 18 the center of curvature. From the equation it is seen that if any two of the distances are given the other can be found. Thus solving (1). Spherical Aberration; Caustics.--The assumption that rays emitted from a single point intersect also after refracting in a single point is virtually correct with a lens whose aperture, that is, the angle obtained by joining the edges to the principal focus, does not exceed 10 or 12. Ques. What is the efiect of a larger aperture? Ans. The rays which traverse the lens near the edge are refracted to a point F on the principal axis nearer the lens than the focus of the rays G which pass near the axis. FIG. 3,807.--Efl'ect of spherical aberration: it produces a lack of sharpness and definition of an image, If a ground glass screen be placed exactly in the focus of a lens, the image of an object will be sharply defined in the center but indistinct at the edges, and if sharp at the edges, it will be indistinct at the center. This effect is very objectionable, especially in photographic lenses._ To avoid this, a disc D with a hole in the center is placed concentric with the principal axis of the lens, thus only the central part of the lens is used. That is to say, the rays farther from theprincipal axis are refracted more than those near this 'axis. Ques. What ill efiect is due to spherical aberration? Ans. The image is slightly blurred. Ques. How may this be avoided? Ans. By means of a "stop," that is to say, a disc with a small hole in it placed in the path of light, as shown in fig....show more

Product details

  • Paperback | 86 pages
  • 189 x 246 x 5mm | 168g
  • Rarebooksclub.com
  • English
  • Illustrations, black and white
  • 1236993349
  • 9781236993342