Screen E-Book (.PDF) - MacDermid Autotype

Getting the right exposure(or number of units) for that particularstencil/mesh/light source combination.Example: 0.7 x 10 minutes = 7 minutesCorrect factor x test exposure = CorrectExposureIf there is still a colour change betweenFactor 0.7 and Factor 1, this indicates anunder-exposed stencil, DOUBLE the originaltest exposure, and repeat the test.The Exposure Calculator can also be usedto assess printed edge definition (straightness/clarity of the printed edge) and printresolution (fineness of detail achievable).The target is designed to allow the userto select the best angle to position thefilm positive stencils in order to avoid “sawtooth” and mesh interference. Resolutionis checked by assessing the degree of “fillingin” at the centre of the target.As part of the Autotype Digital ScreenPrinter software suite, the Digital ExposureCalculator lets you explore many of the effectsdiscussed in this chapter. Althoughit cannot be a precise guide, the generaltrends shown in the software can be helpfulfor thinking through exposure issues.The graphs on the right are particularlyhelpful in understanding what happens tothe dots in the high-light and shadow regions– as you try to improve the situationfor one, you tend to make things worsefor the other. The screen shot shows whathappens if the Rz is set to a very high value– producing a very large change in thedot-gain curve from the exposure.Exposure tips and tricks• Get the right distance between lampand stencil. Too close and you have insufficientexposure at the edges and alsostrong undercutting.Autotype Digital Exposure Calculator70