Journal of the Society of Motion Picture and Television Engineers (1950-1954)

The optical system, indicated in Fig. 1, comprises five stationary lenses and five stationary mirrors, in addition to the moving reflectors mounted in the periphery of the spinning disk. The entire assembly, including the 30-gal reservoir for the hydraulic system, is mounted on a structural steel framework, which in turn is supported on casters. The camera, weighing about one ton with fluid, can be pushed about readily by hand. It has been moved over distances of 100 miles by truck without any need for readjustment of the internal optical system. Optical Design Figure 2 illustrates the Isotran principle in its simplest form. The main difference between this simplest form and the form actually used is the omission of several stationary mirrors, whose only function is to bend the optical path for mechanical convenience. The essential optical components are: (1) an objective lens, (2) the moving mirrors providing image transport, (3) a first refocusing lens, (4) a second refocusing lens and (5) the moving photosensitive film. The objective lens forms a primary image of the subject to be photographed. This primary image is formed at the location of the mirrors that provide image transport. These moving mirrors impart a motion to the primary image, without rotation, as viewed from the direction of the two refocusing lenses and the photosensitive film. This translational motion imparted to the primary image is in a direction at right angles to the optical axis of the first refocusing lens. The purpose of the two refocusing lenses is to gather the light from the moving primary image, to refocus this light to form a secondary and final image on the moving film, and to modify the direction and speed of motion of the secondary image relative to the direction and speed of motion of the primary image in such a way that the .90-DEGREE REFLECTORS 90-DEGREE REFLECTORS Fig. 3. Means of imparting translational motion to reflected ray of light. final image on the film will move at the same speed and in the same direction as the film. Figure 3 illustrates the manner in which the mirrors in the periphery of the spinning disk impart translational motion to the primary image formed by the objective lens, as viewed from the position of the first refocusing lens. In this figure, the solid lines show a pair of mutually perpendicular mirrors in one position, and the dashed lines show the same pair of mirrors in a later position. A single incident ray of light is shown, which may be considered as having come from the objective lens. Two positions are shown, however, for this same ray of light after having been reflected by both mirrors of the pair. The upper emerging ray is in the position corresponding to the first position of the mirror pair, the lower emerging ray in the position corresponding to the second position of the mirror pair. By simple geometry, the second emerging ray may be shown to be displaced from the position of the first emerging ray by a distance twice as great as that through which the mirror pair moves in passing from the position of the solid lines to the position of the dashed lines. In Fig. 3, for both positions of the emerging ray, the incident ray is reflected first from the lower mirror of the pair, then from the upper mirror. At a later stage in the motion of the Miller and Scharf: Isotransport Camera 133