GB1057624A - Scanning mechanism - Google Patents

Abstract

1,057,624. Television optical scanning apparatus. AGA A.B. Nov. 15, 1963, No. 45167/63. Heading H4F. A scanning mechanism for receiving electromagnetic radiation in the visible or infra-red portion of the spectrum comprises a planeparallel refractive prism 1 of polygon shape with an even number of sides which is rotated about an axis 2, a collecting refractive system (not illustrated) which has an image surface 5 located within the prism and the optical axis X of which intersects axis 2, an aperture 6 situated substantially on said optical axis and located just outside the circle 3 generated by the rotating prism and a radiation responsive element (e.g. a photo-electric cell or bolometer) positioned behind aperture 6. When prism 1 rotates, the aperture scans a line in the image surface 5 and when a corner of the prism passes the aperture a momentary retrace occurs. A second component of scan perpendicular to the direction of the first scan may be introduced by including an oscillating mirror in the collecting system or by tilting the axis of rotation 2 of the prism. The Specification discusses the form of image surface 5 that is required if the field is to be scanned without aberration for various values of refraction index for the prism. It is shown that the refractive index should be greater than 2, preferably between 3 and 6 with an optimum value of 4. This requires a substantially plane image surface which the collecting system can readily provide. The side of the prism may be coated to reduce reflection and the corners of the prism rounded to reduce air resistance. The signal derived from the radiation responsive clearcut is applied to modulate the scan intensity in a cathode ray tube scanned in two directions, synchronously with the two scanning components produced by the scanning mechanism.