Aplantic Lens (Gr. a privative and wandering), a lens made in such a way as to correct the spherical aberration. When rays come from a great distance, this may he done by making the curve of a lens parabolic in place of spherical, and in telescopes it is accomplished by careful repolishing by hand and testing. For microscopic and photographic lenses, however, a system of two or even more double achromatic lenses is employed, of which the curves are such that all the rays emitted from one point come to a single focus in a corresponding point. Such a microscopic lens is said to consist of an aplanatic system of lenses, and perfection in this respect is the great problem, now being solved by manufacturers of microscopes and photographic cameras.