Optical and Photographic Problems In the Development and Use of an .f/l .0 Streak Camera Transparent to the Ultra-violet

Abstract

The early stages of the high-voltage spark discharge in air are faintly luminous, most of the emission lying in the ultra-violet. For the purpose of obtaining time-resolved photographs of this growth, a lens consisting of a pair of monocentric spherical mirrors was designed. The system was of aperture f/1 .0 and focal length 2.4 in, and included a rotating-mirror to give an image velocity of O.14 in./μsec. The lens produced an image of spherical curvature of radius 2.4 in. The technique which was developed to produce films moulded to this curvature is described. The image distortion which is introduced by the system in both space and time is calculated. It is shown that relaxation of the film after removal from the camera reduced such errors considerably. Stationary photographs were used to obtain the co-ordinates of the three-dimensional spark track. Techniques for obtaining accurate time measurement and the elimination of perspective effects are described. Some examples of spark photography and quantitative measurements obtained with this camera are presented.