The existence of optimal absorbance levels for absorption spectrophotometry is well known. The corresponding phenomenon in the multiwavelength measurements characteristic of correlation spectroscopy lends itself to a similar analysis. The resulting optimization equation is quite complex, but can be approximated for several simplified cases. For very similar absorbances among the set of used wavelengths, or for a situation where the absorbance multiplied by its weighting factor at a given wavelength is far greater than for all the others, the classical optimum at A = 0.434 still applies. For a uniform distribution of absorbance, the optimal maximum absorption is A = 0.868. The complex general case can be rearranged to calculate, given data at a given pathlength, what the optimal condition involves equal relative error in the largest and the smallest absorbance.
D. E. Honigs, G. M. Hieftje, and T. Hirschfeld, "An Optimization of Detector-Noise-Limited Infrared Multiwavelength Determinations," Appl. Spectrosc. 39, 253-256 (1985)