Aplanatic
Pronunciation : Ap`la*nat"ic
Part of Speech : a.
Etymology : [Gr. (Opt.)
Definition : 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.
Source : Webster's Unabridged Dictionary, 1913