Selection of optical glasses 1: Two materials

A new method of selecting glass combinations for the correction of paraxial chromatic aberration in optical systems has been developed. This new method corrects axial color for at least three wavelengths using two different types of glass, and certain combinations may be found which are corrected at four and five wavelengths. The Abbe number and relative partial dispersions are not utilized in this new approach; instead the Buchdahl chromatic coordinate is used in characterizing the dispersion of the glasses. While the method is of general validity, in this first paper the number of different materials is restricted to two. Thick air-spaced doublets and Mangin mirror designs are presented as examples which demonstrate color correction at three, four, and five wavelengths and which are corrected for spherical aberration and spherochromatism as well. Tables are included listing glass combinations that have favorable power distributions and color correction at three, four, and five wavelengths.