Motion Picture Screen Light as a Function of Carbon-Arc-Crater Brightness Distribution
This paper describes a theoretical method for determining motion picture screen light in a carbon-arc projection system, employing light measurements made directly on the arc crater from various angles of view. The opportunity is thus afforded to study the performance of a given carbon-arc source in optical systems having a much wider variety of collecting angle, magnification ratio, and optical speed than could possibly be assembled for actual optical-bench tests. In this way, it is hoped that the selection of the best possible optical system for a given arc will be facilitated, and vice versa. — Examples of the application of the method to the 8-mm “Suprex” carbon arc at 70 amperes, and to the new 13.6-mm super-high-intensity carbon arc at 290 amperes are given. In each case the analysis has been extended for illustrative purposes over a wider range of optical systems than is of present practical interest. However, the general conclusions thus made possible were considered of sufficient theoretical interest to justify this otherwise impractical consideration. For instance, it is indicated that, particularly with the larger crater, the greater lumen pickup of a high collecting angle does not always result in more light on the screen. — Such practical checks of the method as have been made to date, comparing screen light measurements in complete optical systems with the values predicted by the method, indicate a useful order of accuracy for optical-design purposes. However, the limited scope of these checks is recognized, as is the fact that the calculations do not take screen color variations with focal position into account. — It is hoped that this paper will stimulate others to carry on this same type of analysis, and that the foundation will thus be laid for the most effective combination of carbon arcs with the associated optical systems.
- Print ISSN
- 0097-5834
- Published
- 1947-09
- Content type
- Original Research
- DOI
- 10.5594/J11811