Criteria for Pre-Exposure of Spectroscopic Plates

Criteria are found for the optimum pre-exposure to be used to hypersensitize spectroscopic plates for the spectrophotometry of very weak light sources. The concept of the ratio of line strength to granularity (signal-to-noise ratio) in spectrophotometry is developed. Experimental investigations of the relations between emulsion response, granularity, and exposure yield a simple procedure for determining the pre-exposure which maximizes the ratio of line strength to granularity. This pre-exposure also maximizes the incremental plate density for weak exposures, so that under certain conditions the optimum pre-exposure is the point on the Hurter-Driffield curve at which the first and second derivatives are equal.