Some Applications of Aspherical Lenses in Motion Picture Work
ONE of the most important requisites of a motion picture taking lens is speed. This is, in plain words, the ability to produce on the sensitive film that density which is necessary to produce a useful picture. This speed is given, generally, as the ratio of aperture to E. F.2 The greater the diameter of the effective aperture for the same E. F., the more light passes through the lens, and the shorter is the necessary exposure. Strictly speaking, however, the speed as defined by the aperture ratio is not alone the determining factor for the density of the plate, because the latter depends to some considerable extent upon the number of reflecting surfaces occurring in the objective and upon the kind of glass used. I may refer here to a paper which I read in the Dayton Meeting of this Society in October, 1920. It may therefore happen, that two lenses of the same f value differ in effective speed, and it is also possible that a lens of smaller f value may have the same and even a greater effective speed than another one of higher f value.
- Print ISSN
- 0096-6460
- Published
- 1922-05
- Content type
- Original Research
- DOI
- 10.5594/J12456