Patent GB-501160-A (GB)
Title: Improvements in apparatus for the reproduction of sound films
IPC: G11B7/00
Filed: 1937-10-29
Abstract: 501,160. Optical sound-reproducing apparatus. KOLB, 0. K. Oct. 29, 1937, No. 29620. [Class 40 (ii)] Relates to optical systems for use in souudfilm reproducing apparatus embodying a dual photo-electric device. According to the invention, " normal " sound-films may be utilized in such apparatus having a pair of lightsensitive elements disposed symmetrically about a central axis passing through the optical system and the scanning point, by so projecting a single light beam, serving to scan the entire sound track, that its axis is directed at an angle to the central axis in such manner that the beam falls on only one of the light-sensitive elements. A further feature of the invention consists in utilizing a uniaxial optical system for the reproduction of push-pull or asymmetric records, with the aid of two optical deflecting means serving to project two light pencils having non-parallel axes upon a film, so as to form thereon two half images of a slit, the pencils after traversing the film falling upon separate light-sensitive elements. This arrangement may also be used for reproducing from normal films when desired, by making the two deflecting means movable, so that only one of such members may be operative, and may then deflect the light beam, undivided, on to only one of the light-sensitive elements. Fig. 1 shows a system as first described above, in which for reproducing from a normal soundrecord 6, a beam from a lamp 1 is deflected upwards by a prism 3, in close proximity to a slit 4. An objective 5 forms a linear image 6c extending across the sound track, and the light passes on to only one (7b) of the two cathodes of the'twin-cathode cell 7. In the' apparatus shown in Fig. 3, which is adapted either for use with a push-pull record as shown, or with a normal record, the optical system comprises, in addition to lenses 2, 5, two prisms 3a, 3b, one of which is inverted relatively to the 'other. The prisms, which are arranged close to a slit 4, are mounted in a holder 3c which is laterally adjustable by means of a screw and nut so that the centred plane dividing the prisms may be made to lie on the central optical axis of the system. With this setting, two closely adjacent half images 6a, 6b, of the slit are formed in alignment with each other on the two tracks of the record, and the light passes in oppositely inclined pencils on to the two cathodes 7a, 7b, respectively of the photo-electric cell. A base 3g, on which the holder 3c is mounted, may be held in either of two positions by means of a catch 3h. In the position 'alternative to that shown, the prism 3a covers the entire slit 4, and the apparatus then functions as shown in Fig. 1, when used with a normal record. A modification is described, Fig. 2 (not shown), in which the two deflecting prisms are arranged with their apices together, and the two cathodes of the cell are side by side. Arrangements such as shown in Figs. 2 and 3 may be used in association with a system as described in Specification 462,195, for use with normal or asymmetric records alternatively.