Journal of the Society of Motion Picture Engineers (1930-1949)

1949 HALF-MILLION IMAGES PER SECOND 481 however, elaborated differently than described in the section of this paper on Camera Details. In the device as shown in Fig. 2, an objective lens forms a stationary primary image on a rotating mirror. The revolving reflected beam from the rotating mirror sweeps across the stationary refocusing lenses, which are arranged to focus secondary images at two different positions on the stationary film. As the primary image is stationary, and is located at the center of rotation of the reflected beam, the secondary images are also stationary in spite of the rotation of the beam. Each secondary image is exposed, however, only during the rimary Image Rotating Mirror Stationary Condensing Lens Stationary Refocusing Lenses Stationary Secondary Images -Stationary Film Strip Fig. 2 — Elementary principle of operation. time the reflected beam is sweeping across the refocusing lens corresponding to that image. The arrangement is equivalent to two "still" cameras with high-speed shutters timed to open at slightly different times. The stationary condensing lens shown in Fig. 2 is placed so close to the secondary image that it has little effect on the image. Its function is to condense the reflected beam into the smallest possible area on the surfaces of the refocusing lenses. CAMERA DETAILS In designing a camera suitable for studies of engine knock, some modifications were made on the elementary form shown in Fig. 2. The first such change was to eliminate the condensing lens and to grind the rotating mirror with a concave curvature, allowing the Stationary Objective Lens