GB424042A - Improvements in making sound records photographically - Google Patents

Abstract

424,042. Optical sound-recording. I. G. FARBENINDUSTRIE AKT.-GES., Frankfort-on-Main, Germany. July 5, 1933, No. 19081. Convention date, July 5, 1932. [Class 40 (ii)] Relates to the production of a photographic sound-record of constant width and varying density by means of a light-controlling device adapted to undergo, under the influence of the sound to be recorded, a displacement from its rest position which causes a corresponding variation in the intensity of illumination of the record surface. According to the invention, in order to compensate for distortions due to the gradation of the photographic emulsion used or to the light-controlling device, or to both, there is interposed between the light - controlling device and the record surface an optical device which causes the intensity of illumination to vary irregularly with the displacement of the light-controlling device. The Figure shows an apparatus for carrying out the invention. Light from a suitable source (shown as an illuminated slotted diaphragm a) is projected by a lens b through a slot c on to the mirror d of an oscillograph. The light reflected by the mirror forms an oscillating band g on an aperture e<1> of predetermined shape in a diaphragm e, which is arranged in front of a lens f, this lens forming on the photographic film i a stationary image h, of which the dimensions are constant, but the intensity varies in accordance with the variations in the amount of light transmitted as the band g moves across the aperture e<1>. An explanation is given, with the aid of graphs, of the manner in which the shape of the aperture e<1> is designed, using the characteristic curves of the negative and positive emulsions employed for the recording. Instead of the diaphragm e, there may be used a grey wedge with an irregularly increasing thickness ; or when using a film that is differentially sensitive to light of different wave-lengths, use may be made of a wedge which, in zones of different density, is coloured so as to be suitably absorbent for the different wave-lengths. The recording device used need not necessarily have a rectilinear characteristic, since the apertured screen e or equivalent optical device may be designed to provide the compensation required in this respect. The invention may also be applied in the production from an original record of a copy, by photo-electric means.