GB479846A - Improvements in or relating to optical sound recording systems - Google Patents

Abstract

479,846. Optical sound recording process and apparatus. KLANGFILM GES. Aug. 10, 1936, Nos. 22028 and 22029. Convention dates, Sept. 12, 1935 and Oct. 22, 1935. [Class 40 (ii)] In a process for supervising the recording of sound on a film, the recording-apparatus is arranged to control two different beams of light emanating from a single light source, one beam serving for the sound recording and the other for supervising the sound recording. With such an arrangement the quantity of the supervising light may be made greater than that serving for the sound recording. As shown, light from a lamp 10 passes through a lens 11 and through two different paths through apertures B<1>, B2 in a screen B. The two beams then pass through a lens 12 on to a mirror 13 vibrated in accordance with the sound currents. Aperture B<1> is of rectangular shape whilst the aperture B2 has one edge vertical and the opposite edge of serrated or toothed formation. The beams are reflected by the mirror on to a second screen A-A, the image of the aperture B2 being moved across a slot 20 therein, the light passing through this slot falling on a film to produce the sound record ; whilst the image of aperture B<1> is moved across the edge K of this second screen, the light passing this edge falling on a monitoring photo-cell. The edge K is preferably inclined in relation. to the image B<1> to an extent corresponding to the width of the slot 20. In order to prevent any stray light from the monitoring light beam which may reach the path of the recording light beam producing distortion, the monitoring light is preferably arranged to embrace a spectral range which is photographically not, or only slightly, effective with the film emulsion used. Thus red light or infra red light would be used with the usual film emulsions whilst with panchromatic films a green light would be used. The colour of the light is obtained by inserting a corresponding filter in the path of the monitoring light. A monitoring photo-cell is also preferably selected which is particularly sensitive to the particular light employed, e.g. with a red light a cell having a layer of caesium or caesium oxide is preferably used. When the invention is used in an anti-ground noise recording system, an anti-ground noise shutter or shutters is or are arranged to control the monitoring light and the recording light to the same extent, Fig. 4 (not shown). According to a modification, Fig. 5 (not shown), the screen A-A is dispensed with and a prism is arranged to reflect the monitoring light beam on to the photo-cell.