GB381544A - Improvements in or relating to television scanning apparatus - Google Patents

Abstract

381,544. Television. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, DOWSETT, H. M., 47, Drayton Gardens, Winchmore Hill, both in London, PLAISTOWE, D. L., 21, Oakleigh Park Drive, Leigh-on-Sea, and LEVIN, N., 61, Albert Street, Regents Park, London. July 4, 1931, No. 19338. [Class 40 (iii).] In order to permit the use in a television receiver of a neon lamp having a cathode of a square or other shape different from that (generally rectangular) of the picture scanned at the transmitter, or to produce an enlarged image at the receiver without increasing the size of the scanning disc, the apertures in the scanning disc or drum are made rectangular with their longer dimension radial or at rightangles to the direction of scanning, while the resultant distortion, i.e. the elongation of the image in the radial direction, is compensated by optical means, such as a cylindrical or sphere-cylindrical lens, thereby restoring to the image as viewed the original shape of the pictu e. In Fig. 3 is shown diagrammatically a receiving arrangement for a transmitted picture originally of rectangular shape with its longer dimension vertical, and which has been scanned at the transmitter by a Nipkow disc with square apertures. The rectangle PA represents in the plane of the receiver Nipkow disc (not shown) the distorted area scanned by the elongated apertures such as A, NTC representing a rectangular neon tube cathode. The compensation afforded by the cylindrical viewing lens CL is sufficient to give to the virtual image A<1> of the aperture A a square shape as employed at the transmitter, and also to give to the virtual image VI of the rectangle PA the rectangular shape of the original picture proportionately enlarged. A receiving arrangement in which the picture is projected upon a screen 5 is illustrated in Fig. 4. the light from the neon lamp after passing through the rectangular apertures 1 of the disc 2 being projected by a sphere-cylindrical lens system 3 as square elementary screens upon the screen. Such an arrangement may also be used at the transmitter for scanning with a disc having elongated rectangular apertures. If, in addition to elongating the apertures, their width is reduced proportionately to pass the same amount of light as square apertures, the number of apertures in the disc may be increased and a finer scanning be effected, the reduced height of picture again being compensated by the optical means.