aplanat

from The Century Dictionary.

• noun A system of lenses invented by Adolph Steinheil, in 1866, for use in photography, consisting of a biconvex crown-glass lens placed between two concavo-convex lenses of flint-glass.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A lens that has been corrected for spherical aberration and coma in order to produce a rectilinear image.