A Point Light Source for Laboratory Use

THE term “Point Light Source” is frequently made use in the calculation and discussion of optical matters. It should always be kept in mind, however, that such a source is only hypothetical and represents a theoretical limit that is unattainable by any means whatever. In a quite similar manner, textbooks on optics give explanations and even formulae for calculating lenses on the basis of a lens with infinitesimal or zero thickness. These theoretical concepts are, of course, of considerable value in working out an optical system, and their use for such purposes should not be decried. In fact, some such assumptions are almost a necessity for the practical development of applied optics, but the fact remains that they are only hypothetical assumptions which can never be realized, and allowance must always be made for the finite or actual dimensions of the real physical light source. The astronomical telescope may perhaps be an exception, for the fixed stars as seen from the earth are point light sources for all but the most extremely delicate apparatus. In the observation of stars, however, another difficulty is encountered, i. e., the image of the star is not a point but has quite appreciable dimensions due to diffraction.

Print ISSN

0096-6460

Published

1921-10

Content type

Original Research

DOI

10.5594/J12473