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

3CRLLN Fig. 1. Optical arrangement of schlieren system. Fig. 2. Eidophor liquid as diffracting agent at image plane. the workability of the basic ideas and led to the development of later models which performed satisfactorily. Figure 1 is a schematic of this optical arrangement. The positive crater A of the arc lamp together with condenser lens B produces uniform illumination of the plane C; the light-modulating or controlling medium is placed in this plane between two bar-and-slit systems F and G. A field lens is so arranged that it images system F upon the bars of system G, at the same time insuring correct illumination of each and every point on the controlling medium. By way of example, the point H is illuminated in such a manner that the incident light beams passing through the slits of system F impinge upon the opaque bars of system G. The image point H is located in the image plane C of the objective lens D. This projection lens would thus image the point H as point H' on a projection screen E. This is however impossible since the illuminating light beams are blocked off by the bars of system G. If, however, the control medium located in the image plane G is deformed in a suitable manner, diffraction of the incident light can be effected, and the diffracted parts of the beams may be made to pass through the slits of system G and reach the projection screen as image-forming light. Figure 2 shows an oil layer of minute thickness at the image plane C (shown also in Fig. 1). This layer of liquid, called the Eidophor liquid, takes the place of the usual motion picture film in the film gate, as far as the optical 338 April 1953 Journal of the SMPTE Vol. 60