APLANATIC

Ap′la‐nat″ic (�), a. [[Gr. ἀ priv. + � disposed to wander, wandering, � to wander.]] (Opt.) 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.