This International Standard specifies two reference wavelenghts to be used for the characterization of optical materials, optical systems and instruments, as well as ophthalmic lenses. It defines the associated principal refractive indices and principal dispersion, as well as the Abbe number with regard to this reference wavelength and the principal dispersions.
DS/EN ISO 7944:1999 history
1999DS/EN ISO 7944:1999 Optics and optical instruments - Reference wavelengths