aplanatic

Ap`la*nat"ic, a. Etym: [Gr. (Opt.) Defn: Having two or more parts of different curvatures, so combined as to remove spherical aberration; -- said of a lens. Aplanatic focus of a lens (Opt.), the point or focus from which rays diverging pass the lens without spherical aberration. In certain forms of lenses there are two such foci; and it is by taking advantage of this fact that the best aplanatic object glasses of microscopes are constructed.

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