Expressions are derived for the primary longitudinal and transverse chromatic aberrations of a lens system as summations of terms over all the singlet components of the system. Each term in these summations is the product of the partial dispersion of the glass of the lens with a certain coefficient which is easily calculated from the data of a paraxial trace, and specifies the contribution made by the lens to the corresponding primary chromatic aberration of the final image. The coefficients are called the primary chromatic coefficients of the system. In addition, the coefficients provide a rapid means of analyzing the complete secondary spectrum of the system, and afford a clear guide to the adjustment of the primary chromatic aberrations insofar as it is desired to do this by the selection of different glass types.
F. D. CRUICKSHANK, "On the Primary Chromatic Coefficients of a Lens System," J. Opt. Soc. Am. 36, 103-103 (1946)