GB484251A - Improvements in or relating to sound recording - Google Patents

Abstract

484,251. Optical sound recording apparatus. RADIO CORPORATION OF AMERICA. April 1, 1937, No. 9313. Convention date, April 29, 1936. [Class 40 (ii)] [Also in Group XX] An apparatus for recording sound by means of a narrow band of light frequencies, preferably ultra-violet light, comprises a light source 10, a light modulating device 14, means for directing the light from the source to the modulating device and thence to the record film 18, a colour filter in the path of this light, and means for directing light from the source to the modulating device and thence to a view point or monitoring screen 21 independently of the colour filter. Lenses 11, 19, 15, 17 and apertured plates 12, 13, 16 are provided in the paths of the light. The colour filter may be placed at 22 before the modulating device or at 23 after the modulating device. In the first case, a red filter 24 is placed before the modulating device in the path of the monitoring beam. This beam is reflected to the screen 21 bv a mirror 20. The wave length of the recording beam may be between 3200 and 4000 Angstrom units. The lenses are made to have the same focus for the ultra-violet light used as for a visible part of the spectrum, for example green, to facilitate focusing. The film used should be absorbent to the part of the spectrum used, whether green, blue, violet, or above 4000 Angstrom units. This is ensured by dyeing the film in known manner. The Specification as open to inspection under Sect. 91 comprises also a number of curves relating to gamma values, development times, densities, and transparencies for various lights, and mentions films with emulsions of ¢ mil. in thickness. This subjectmatter does not appear in the Specification as accepted.