Projection Offset - A Review of the Optical and Photographic Requirements.

Projection offset, the use of reduced sized negatives as the intermediate between input copy and the printing plate, is attractive as a material and labor savings approach to offset lithographic printing. An analytical study of such a concept was completed to assess the technical requirements that are placed on the optical and photographic materials involved. Using quality criteria defined for both line and halftone copy, this study shows that the factor limiting the performance of projection offset systems is clearly optical performance of the reduction and projection stages. An understanding of, and criteria for, unique film and plate exposure aim points are also developed. The sensitometric and optical characteristics associated with selection of optimum intermediate films are discussed and specific recommendations given. The paper also includes results of a practical test conducted using a production projection offset system. These tests include the satisfactory reproduction of halftone images at a reduction/projection magnification of 5.75 times. The paper also includes results of a practical test conducted using a production projection offset system. These tests include the satisfactory reproduction of halftone images at a reduction/projection magnification of 5.75 times.