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

of the spinning disk and through the axes of the various optical parts, showing the important mechanical details of this Isotran camera. In this sketch two cylindrical lenses are shown which were not included in the diagram of Fig. 5. The cylindrical lens near the focal plane of the primary image causes the primary image to conform to the cylindrical surface traced by the lines of intersection of the pairs of mutually perpendicular mirrors in the periphery of the spinning disk. Upon the second passage of the light beam through this cylindrical lens, after reflection from the moving mirrors, the light rays are restored approximately to the condition corresponding to a flat primary-image plane. The cylindrical lens near the moving photosensitive film causes the final image to conform to the cylindrical shape of the moving film. The emulsion of the photosensitive film, carried on the inner surface of the ledge, is very slightly closer to the axis of spin of the disk than are the lines of intersection of the moving, mutually perpendicular, mirrors. Any linear dimension of the final image must, correspondingly, be slightly less than half the same dimension in the primary image. Ready adjustment of the final image to the exact size required is made possible by the condition of parallelism of the optical axes of the two refocusing lenses. The three stationary mirrors located in the optical path between the two refocusing lenses are mounted on a single bracket, which can be adjusted in a direction parallel to the axes of the refocusing lenses. If the first refocusing lens is held stationary while the bracket mounting the three stationary mirrors is moved outward, and if the second refocusing lens is moved along its optical axis in such a manner as to retain a sharp focus of the final image on the film, the size of the final image changes. The spinning disk is axially symmetrical. A second optical system is now being constructed, which with the present system will allow photographs to be taken simultaneously on film strips mounted on the inner surfaces of the ledges on both sides of the disk. This second optical system will be located at a position along the circumference of the rotating disk 25° away from the present system. The second optical system will be reversed from right to left relative to the first optical system shown in Fig. 1 . The possibility of taking two series of photographs of the same phenomenon, with an absolute chronological correlation, will be of great advantage in the study of combustion in an engine cylinder, and possibly also for other applications. In the study of combustion, schlieren photographs will be taken at the same time as direct-flame photographs. The results should answer a number of questions relative to the meaning of phenomena observed in the schlieren photographs but not seen in direct-flame photographs. Optical-Mechanical Details The lenses used in the present optical system of the camera are all standard products purchased from the Bausch & Lomb Optical Go. The objective lens is a Tessar, //4.5, of 139-mm focal length. The first refocusing lens is a Baltar, //2.7, of 152-mm focal length; the second refocusing lens is a Baltar, //2.3, of 75-mm focal length. These lenses were selected partly on a basis of high optical speed, but primarily on the basis of optimum resolution. For the second optical system of the camera, now under construction, primary emphasis will be laid upon high optical speed, with good resolution as a secondary consideration. At the same time that the present optical system is used for schlieren photography, the second system will be used for directflame photography, that is, for photog 136 February 1953 Journal of the SMPTE Vol.60