. . "achromatized" . . . "Oil-spaced doublet" . "achromatic lens" . . "Clark doublet" . "achromatic" . . "achromat" . . . "Steinheil doublet" . "Achromatic lens" . "achromatic objective microscope" . "Fraunhofer doublet" . "Littrow doublet" . . "achromatic objective lens" . "achromatic doublets" . "achromatic doublet" . "achromatic refractor" . "achromatic refracting lens" . "Achromatic lens" . "Achromatic" . "achromatic glasses" . "achromatically" . "achromatic telescope lenses" . .