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

considerations are concerned. This oil layer, by way of illustration, might be supported by a glass plate. It has been pointed out that the incident illumination of every image point is blanked off by the strips of the bar system shown as G (in Figs. 1 and 2). Since every point of the oil layer is illuminated and since each light beam traversing the layer is prevented, by the bars of G, from reaching the lens when the oil layer is of uniform thickness and is homogeneous, then under this condition no light will reach the screen. There remains then the problem of creating an image record in the form of some optical inhomogeneity which will cause the oil layer, point by point, to diffract the light beam through the slits of G. This is done by means of an electron beam from an electron gun which scans the oil layer and forms thereon a picture raster. The electron gun deposits electric charges point by point corresponding to the scanned picture and these charges cause minute corrugations in the surface of the oil layer. Where the surface is corrugated as at HI on surface G in Fig. 2, the light rays issuing from any such image point are diffracted, and part of the light which normally illuminates the bars of stop G then passes through the slits and produces illumination at the conjugate point H'i on the projection screen. This illumination will become more intense the more the Eidophor liquid surface is distorted, and we have therefore a means of reproducing point by point and line by line a television picture raster on a full-sized screen. Figure 3 shows the relation between the distribution A of brightness along the line of the image to be reproduced and the wave-shaped deformation B of the surface of the Eidophor layer. The deviation of the envelope of the deformation curve from the original smooth surface is proportional to the desired brightness value. The principle of the Eidophor method Fig. 3. Relation between distribution of image brightness (A) and deformation of Eidophor surface (B). resides in modulating the cathode beam scanning the Eidophor surface by the video signal in such a manner that the deformations are proportional to the instantaneous value of the video signal. These wave-shaped deformations are brought about by the periodically varying distribution of electrical charges as stated above. These charges deposited on the oil surface by the cathode beam cause deformation by means of electrostatic forces. The wavelength of these deformations is always constant and lies in the neighborhood of 0.1 mm. The height of the waves is proportional to the video signal. As the illumination of the image points on the projection screen is always proportional to the height of the waves at the corresponding point on the Eidophor, the distribution of light over the projection screen corresponds to the video signal and thus to the object to be reproduced. The deformation commences at the moment in which the cathode beam scans a particular point of the image. By a suitable choice of the conductivity and viscosity of the Eidophor oil, it is possible to conserve the deformation for a considerable part of the image-scanning period so that it disappears but shortly before the occurrence of the succeeding scanning. In other words, the illumination of the projection screen is maintained for this part of the scanning period ; this represents a substantial light storage Earl I. Sponable: Eidophor System 339