Camera Shutters*

Abstract

An extensive program of research into characteristics of shutters, begun in 1941, has resulted in a series of definitions and test methods for between-lens and focal-plane type shutters which have been adopted by the ASA. The characteristics of these two types of shutters, and of louvre shutters, are reviewed, and the important distinction between effective exposure time and actual (or motion-stopping) exposure time in these two shutter types is clarified. The oscillographic test method for between-lens shutters is described and depicted via photograph and schematic diagram. The strobotac and drum tester method for focal plane shutters are summarized, as is a method for testing louvre shutters.The effect of inefficient between-lens shutters on optical performance, effect of a glass pressure plate on efficiency of focal-plane shutters, and equations for the two types of distortion caused by focal plane shutters are discussed. The utilization and advantage of shutter speed in aerial cameras to reduce the deteriorative effects upon definition caused by forward aircraft speed, angular motion of the aircraft about its axis, and camera vibration are discussed.The shutterless strip camera and the corollary principle of image speed compensation with moving-film magazines in conventional cameras, and the potentialities of this important new development, are described.The impetus of wartime necessity resulted in development of several new shutters, improvements in others, and consideration of many more types. The Langer multiple-slit focal plane shutter, shutters based on birefringent phenomena, multiple-disk between-lens shutters are considered. Shutter leaves of Be-Al alloy were tried, with conspicuous success. The work done by Mitchell in doubling the speed of the 6-in. K-17 shutter and a detailed analysis of research results obtained in improving the K-22 focal plane shutter are presented.A louvre-shutter for the 48-in. f:6.3×18 lens was built at the Photographic Laboratory. Photographs and a schematic diagram of this high performance shutter are included. A doctrine of tactical usage and development for shutters has been formulated; mapping cameras will continue to use between-lens shutters, as will night cameras, but the very large day reconnaissance camera will use focal plane shutters exclusively. A list of seventeen memorandum reports, which cover in detail the work summarized in this paper, is appended.