GB329664A - Improvements in or relating to television apparatus and the like - Google Patents

Abstract

329,664. Baird, J. L., and Television, Ltd. Feb. 19, 1929. Television.-The invention comprises various improvements relating to the apertures in a scanning disc. The linear distance between adjacent scanning apertures or mirrors may be uniform, so that the angular distance between them is greatest for apertures nearest the centre of the disc (Fig. 1, not shown). The apertures 36, Fig. 3, near the end of the spiral may be radially deeper than those, 35, near the middle. The depths may be graduated (Fig. 2, not shown) or of two different sizes, Fig. 3. An alternative method of equalizing the apparent lengths of the scanning-paths is shown in Fig. 13. The scanning disc 40 is cupped and may be provided with a rim (Fig. 4, not shown) in order that it may be light and rigid : or a flat or cupped disc flange at its circumference (Figs. 6, 7, not shown). The cupped disc 40 may be used at the receiver in conjunction with a fluctuating light source 71 and a lens 70 whose focal length is greater than its distance from the disc. The scanning apertures are in this case angularly equidistant, so that the linear distances between them are greatest towards the outer edge of the disc; but owing to the unequal magnification arising from the curvature of the disc, which produces inequality in the distances of the apertures from the lens, the apertures appear to the eye 73 to be linearly equidistant. In a modification (illustrated as applied to a transmitter in Fig. 15, not shown) a diverging lens is placed on the convex side of the disc 1. The scanning apertures may have bevelled edges as shown at 54, Fig. 8, in order to produce a clear-cut beam of light and to avoid parallax effects; or the thickness of the disc may be reduced in the neighbourhood of each aperture (Fig. 13, not shown). The scanning apertures 61, Fig. 9, may be covered by an annulus 62 of ground glass or celluloid, in the plane of which the image is formed at the receiving station; in this way parallax effects are avoided. Alternatively, each aperture 61 may be covered by a small translucent plate, (Figs. 10, 11, not shown). Specification 265,640 is referred to.