a. [f. Gr. ἀπλάνητ-ος free from error (f. ἀ priv. + πλανά-ειν to wander) + -IC.] Free from aberration; spec. applied to a compound lens which is free from spherical aberration or divergence of rays of light from the focus.
1794. G. Adams, Nat. & Exp. Phil., II. xxii. 468. As … [Blair] conceives that he has thus removed the aberration, he distinguishes his instrument by the term Aplanatic.
1867. J. Hogg, Microsc., I. ii. 26. An ‘aplanatic doublet,’ consisting of a double-convex lens and a meniscus.
1869. Tyndall, Light, § 165. A spherical lens cannot be rendered aplanatic.
