Abstract: The invention relates to a method and an apparatus for reducing the diameter tolerance of a laser beam. A lens (3) is positioned so that one of the focal planes of the lens (3) is in the region of a limit (5) of the Rayleigh range of the beam (19). The lens (3) forms a second beam waist at a position (6), where a modulator (10) is placed. The beam (21) then passes through beam expansion apparatus (11,12,13) before being collimated by a lens (14). The collimated beam (25) is then focussed to a third beam waist at the recording drum (17), via a lens (18) and mirror (15).

Abstract: A method and apparatus for controlling the spectral components of a light beam are described. The apparatus comprises means (3-7) for generating a collimated light beam; means (9) for dispersing the collimated beam; a mask (1) including an aperture (2) the size of which is such that a portion of the dispersed beam passes through the aperture in use; and movement means (not shown) for causing relative transverse movement between the light beam and the aperture. A memory (not shown) is provided for storing in use a profile of the relative transverse movement between the light beam and the aperture (2) required to obtain a desired spectral response in the transmitted light beam, the movement means being responsive to the stored profile to cause relative transverse movement in accordance with the predetermined profile.

Abstract: Apparatus for splitting a light beam into a plurality of parallel beams of equal intensity comprises at least two blocks of isotropic light-transmissive material, each block having one major face, on which the input beam is incident, coated to be partially transmissive, and an opposite parallel major face which is silvered. The blocks are arranged in series so that the input beam, on reaching the first block divides into a reflected part and a transmitted part which enters the block and, after total internal reflection, provides an output beam parallel to the reflected part of the first beam, each subsequent block receiving all parallel beams from the preceding block or blocks. Optical means may be provided in the beam path to ensure that each beam entering each block has equal S- and P- polarization components.

Abstract: To produce a plurality of parallel light beams from a single input beam, the input beam is incident on a partially transmissive face of a triangular prism, the other two faces of which are silvered. The input beam strikes the partially-transmissive face at such a position and at such an angle of incidence that it gives rise to only two parallel emitted beams, part of the emitted light arising from internal reflections at both silvered faces. A number of such prisms may be arranged in series so that the n.sup.th prism receives 2.sup.n-1 beams and emits only 2.sup.n parallel output beams.The partially-transmissive face or faces may be coated to give rise to output beams of substantially equal intensity. In one form, each beam entering each prism has equal S- and P-polarization components.

Abstract: Scanning apparatus for generating signals representing color components of successively scanned picture elements of an original colored image comprises a light source (1); means (42,45) for causing relative movement between the original image (3) and a light beam generated by the light source (1) whereby successive picture elements of the original image are scanned. Means (13) for generating a sharp light beam for each color component of each element and an unsharp light beam for at least one color component of each element are provided. Common detection means (10) receives the sharp and unsharp light beams and provides corresponding output signals. Sequencing means such as a filter wheel (13) causes the sharp and unsharp beams sequentially to impinge on the detection means (10).

Abstract: This relates to a method of image reproduction in which detail enhancement is carried out using sharp and unsharp signals (S and U), for example in accordance with the expressionP=K (log U- log S)- log Swhere P is the derived picture signal and K is a constant. To reduce the disparity between the fringe amplitudes and steepness on the two sides of a density boundary, the above expression is modified, in accordance with the invention toP=K {log[U+L (U-S)]}-(K+1) log S.Another expression involving the same subtractions of sharp and unsharp signals as the first expression above but in a form suitable for use with signals which have been compressed to represent luminance, is modified in accordance with the invention in a similar way.

Abstract: A beam splitter is disclosed in which a light beam entering a block of light-transmitting material is internally reflected a plurality of times between a pair of parallel sides, one side being coated to enhance such internal reflection and the other side having in the direction of its length a succession of areas which are differently coated to control the amount of the beam which is reflected internallly and the amount of the beam which emerges; a plurality of parallel emergent beams of substantially equal intensity can be obtained in this way. The application of such a beam splitter to an image-reproducing system is described, the beams contributing to the formation of half-tone dots in the image.

Abstract: In an image-reproducing system in which a number of parallel light beams contribute to the formation of half-tone dot areas on a record medium and scan over the record medium together, a reversing prism is included in the beam path to permit the line fit or line overlap to be closely controlled. The prism also adjusts the spacing between beams in the scanning direction which is provided when a coherent light source is used to avoid interference between adjacent beams.

Abstract: In an image-reproducing system in which a number of beams scan over a record medium together and contribute to the formation of half-tone dots, an anamorphic system is included in the beam path to match the beam cross-section to the shape of mask apertures in the light paths and to compress the length of the line of beams, transverse to their direction.