Details:
Summary:
Experience when imaging the popular lithographic diazo oxide sensitized grained positive plate has indicated that the halftone reproduction can be inconsistent and that this can lead to the adoption of local standard plate control scales of dubious value. Investigation has shown that it is the process variables as indicated by recent screenless imaging theory that cause the inconsistencies and these variables are dealt with together with their resultant effects. It is concerned with four types of plate control scales. Investigation has shown that it is the process variables as indicated by recent screenless imaging theory that cause the inconsistencies and these variables are dealt with together with their resultant effects. It is concerned with four types of plate control scales. As well as demonstrating that any specimen of positive plate does not (as often assumed), possess a fixed photo-speed, and that its photo-speed changes according to the process variables, it is shown that neither continuous tone scales nor macro line (or dot) scales can ensure accurate imaging. To maximize accuracy the process variables need to be accurately controlled and it is suggested that a control device comprising a continuous tone scale together with a macro line (or dot) scale be employed on every plate. The above is dealt with in terms of the effective sensitivity and reference is made to the relationship of screenless theory when imaging such plates.