Selection of optical glasses for cemented doublet mangin mirrors.

The variation of the coma and the zonal spherical aberration with the refractive indices and dispersions of the glasses of an achromatic cemented doublet Mangin mirror corrected for spherical aberration is discussed. Approximate expressions for the former two aberrations in terms of the glass constants are given, and it is shown how these expressions may be used for the selection of a glass combination which effects simultaneous correction of these aberrations as far as is possible with the available optical glasses.