GB388820A - Improvements in or relating to optical systems for sound translating apparatus - Google Patents

Abstract

388,820. Reproducing sound from optical records. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.-(Assignees of Smythe, E. H. ; 1162, Monadnock Block, Chicago, U.S.A.) Sept. 4; 1931, No. 24912. Convention date, Sept. 15, 1930. [Class 40 (ii).] In an optical system for reproducing sound wherein a beam from a light source is focused by a lens system on to a slit and passes through another lens system which focuses it on to a film, the angular subtense of the beam directed on to the film is smaller than usual whereby loss of resolution of the higher frequencies when the film becomes displaced laterally in its travel is reduced. The slit between the lens systems may be reduced in depth below the usual and the beam directed thereon at a wider angular subtense to maintain the normal slit factor, that is the product of slit depth and angular subtense of beam, and the lens system directing the beam on the film may magnify the slit image at the film to normal size. The Figure shows the arrangement ; the angular subtense 23 of the beam directed by the objective lens system 6, 7, 8 on to the film is reduced below the usual, for example to 17‹, and the slit 5 has a reduced depth and the angular subtense 21 of the beam directed thereon by the lens system 2, 3 is increased, for example to 26‹, a magnified image of the slit being produced on the film by the lens system 6, 7, 8.