GB1338478A - Contact screens - Google Patents

Abstract

1338478 Half-tone screens HOWSONALGRAPHY Ltd 23 March 1972 [31 March 1971] 8340/71 Heading G2M A contact screen includes a first zone of maximum density and a second zone of minimum density, a pattern of crossed lines which constitute one of the zones and form the boundaries of areas having other densities (including the other zone), each of said areas including dots arranged around its centre, the vignetted density of each dot differing from that of each of the other dots in the same said area, the remaining part of each area having a vignetted density which varies from a value nearer to that of said zone constituted by the pattern of crossed lines at the centre of the area to a value or values nearer that of the other zone at location nearest the lines forming the boundaries of the area. As shown Fig. 1 a negative screen comprises transparent lines A defining areas comprising (a) dots B, B1, B2 and B3 of different densities and (b) a crossshaped area A1 which increases in density from its centre; the screen produces in accordance with the degree of exposure the dot shapes shown in Fig. 2. A positive screen which is the reverse of the negative screen of Fig. 1 is also disclosed Fig. 5, (not shown). The invention also relates to patterns for the photographic production of preferred positive and negative screens.