GB931450A - Improvements in telecine apparatus - Google Patents

Abstract

931,450. Television. BUSH & RANK CINTEL Ltd. March 20, 1961 [March 18, 1960], No. 9650/60. Class 40 (3). In an arrangement for scanning a continuously moving cinematographic film to produce corresponding television signals either by projecting an image of the film on to a picture signal generating tube (Fig. 1, not shown) or by projecting an interlaced scanning raster from a flying-spot scanner 24 (Fig. 12) through the film 1 and on to a photo multiplier 25, a motion arresting rotating transparent polygonal prism 8 being employed in each case, differences in the brightness of adjacent lines due to imperfections in the optical system are reduced by limiting the total amount of light by means of opaque members 19, 20 (see also Fig. 5). Such imperfections, mainly spherical aberration, result in a variation of the distance between the centres of the series of " patches of light " 15, 16, Figs. 2 and 3 (images of the aperture of lens 6 formed by lens 7 via the prism 8) as the prism 8 rotates this distance varying from the perfect case in which it is equal to the distance d (Fig. 2) between the knife edges 9, 10 to a distance d+ #d (Fig. 3) which depends on the distance of the point considered from the optic axis of the system and therefore also varies as the prism 8 rotates. Fig. 6 shows how the introduction of one of the opaque members, in this case 19, results in the production of a " shaded " area 21, thus preventing light from the portion of the " patches " 17, 18 obscured thereby from taking part in the scanning operation. When the separation of members 19, 20 is equal to that of the knife edges 9, 10 (as modified by lens 11), the obscuration produced falls from a maximum for marginal image points to zero for points on the optic axis which is the derived result. A plurality of pairs opaque members such as 26, 27 and 28, 29 (Fig. 9) may be employed instead of a single pair. When a single pair is employed (see Fig. 11) they may be rotated (in opposite directions) about their longer axis by means of gears 34, 35, pinion 342, idler gear 36 and a gear 37 driven by the prism 8, the arrangement being such that the opaque members 30, 31 rotate at half the rate at which the facets of the prism replace each other in the knife-edge gate 9, 10 and present minimum obstruction when a facet lies parallel to the plane of the knife edge. To reduce variations in the mean level of the signals produced due to the presence of the opaque members, a compensating waveform of triangular shape and of picture repetition frequency may be employed.