Reciprocity Failure in Orthochromatic Litho Films.

Reciprocity failure is shown to be a most significant factor in the exposure of orthochromatic litho films. An experimental method is described for measuring the variation of emulsion speed as a function of exposure time using sensitometric exposures made in a process camera. Response curves are given for typical films used in the trade. Considerable change in speed relationship is noted among the various materials as exposure time is increased from 7.3 to 480 seconds. The implications for line and halftone photography are discussed in terms of the exposure times required, with other exposure conditions identical, to produce the same practical result on films which differ in their reciprocity behavior.