Aplanatic

[Sarah]

Having two or more parts of different curvatures, so combinedas to remove spherical aberration; -- said of a lens. Aplanatic focusof a lens (Opt.), the point or focus from which rays diverging passthe lens without spherical aberration. In certain forms of lensesthere are two such foci; and it is by taking advantage of this factthat the best aplanatic object glasses of microscopes areconstructed.