Aplanatic focus Meaning, Definition & Usage

Definitions
  1. 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.
Definitions
  1. . (Opt.) See under Aplanatic.

Webster 1913