Abstract: A viewing screen is described, in particular the screen of a display tube, which has excellent anti-reflective properties and a method of making this screen anti-reflective. In this method the outer surface of the screen is mechanically roughened in conformity with specific requirements and subsequently an anti-reflective coating of constant thickness is applied to the roughened surface.

Abstract: Providing a transparent layer of an oxide of an element from group IVa of the Periodic Table, notably TiO.sub.2, by providing a substrate with a solution of a compound of the element which upon heating is converted into the relevant oxide, drying the film and heating the dried film so as to form the transparent layer of the oxide. The oxide thus obtained is a form having a comparatively low refractive index. By heating the product, after providing the film, rapidly to a temperature of above 700.degree. C., preferably above 1,000.degree. C., keeping it at this temperature for some time and then rapidly cooling it again, a modification having a higher refractive index (for example, for TiO.sub.2 rutile) is obtained.

Abstract: In a tunable Fabry-Perot interferometer, the supports for two parallel mirrors consist of bundles of optical fibers with the mirrors being provided on the ends of the fibers. This structure may be used advantageously in an X-ray display device wherein the structure is located between the display screen on which the visible X-ray image is displayed and a television camera tube. By using the Fabry-Perot interferometer as a light attenuator in such a device, problems where the camera tube is overridden when making an X-ray record can be prevented by causing the reflection coefficient of the mirrors in the visible range of the spectrum to be 99% or more. Also, the half width of the transmission wavelength pass-band of the Fabry-Perot interferometer can be made less than 50 nm.