Screen E-Book (.PDF) - MacDermid Autotype

Figure ii. The overlayedpattern fromFigure i, but shownin colour.Figure iii. Moiré when thesame two patterns are overlayedat different angles, inthis case 5°.The two originals are Cyan and Magenta.You see Blue lines where they fall on topof each other and stripes of C & M wherethey fall in between each other. If the moirécomes from the railings of a bridge asyou drive underneath you see a movingmoiré because the front and rear railingsshift in relative position. The moiré patternstays the same, but the dark and light areasmove along in sequence.96To get a moiré you need regular patternswhich differ in some way. For the railingsexample the difference was in the spacing.In the next example the difference is in theangle:The spots of the top left are combined with the spots of the top rightinto the resultant pattern bottom left. The moiré calculated by thecomputer model is shown bottom right and closely matches the observedpattern, with a regular repeated pattern of 6.4 lpi (2.5 lpc) andan angle of 2.5° produced by combining a 0° and 5° screen.You can get moirés from just about any regular patterns. Here’s whathappens when you mix circles of different spacing: