The original purpose of this investigation was to explore the possibility of providing a spectrophotometer with automatic means for correcting the error that results when a continuous source is used with a monochromator having slits of finite width. In connection therewith, it was necessary to make what appears to be the first rigorous analysis of slit-width errors. The results of this analysis can be applied to the experimental determination of any functional relationship when the size of the “probe” is significant.
ARTHUR C. HARDY and F. MANSFIELD YOUNG, "The Correction of Slit-Width Errors," J. Opt. Soc. Am. 39, 265-270 (1949)