GB1353739A - Light exposure means for shadow or contact printing - Google Patents

Abstract

1353739 Lighting arrangement for contact printing RANK ORGANISATION Ltd 3 Nov 1971 [12 Aug 1970 19 March 1971] 38809/70 and 7288/71 Headings G2A and G2J Light exposure means, for use in shadow or contact printing, comprises a light source arranged to provide, in a printing plane, an effective brightness distribution having a bright zone surrounding a central less bright zone, this distribution being such that when a mask is illuminated in the printing plane under conditions of transitional Fresnel-Fraunhofer diffraction, this being the diffraction which is observable at a distance from a coherently illuminated line or slit of the same order as the line or slit width, the illumination condition produced by the light incident on any given part of the mask produces diffraction patterns which tend to cancel each other over part of said patterns. In the embodiment of Fig. 4, light from a point source 1 is reflected through 90 degrees by an element 5, passes through a collimator 7 and finally through a wedge prism 6 which is rotated by a motor 8 and belt drive 9. As the prism rotates the emergent collimated light beam performs a conical scan of a mask 2 and lightsensitive substrate 3 to produce the bright zone surrounding the less bright zone. Alternatively the positions of the prism and collimator are inter-changed Fig.3 (not shown). In other embodiments the conical, or a cylindrical scan, is achieved by placing a rotatable mirror Fig. 5 (not shown) or a rotatable rhomb prism Fig. 6 (not shown) in the light path. In further embodiments, which avoid the use of moving components, the beam from a point light source is split into several component beams, arranged in an annulus, by a multiple prism Figs. 7 and 8 (not shown) and by an annular array of reflectors Figs. 9 and 10 (not shown).