\Ap`la*nat"ic\, a. [Gr. 'a 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.