Hypertext Webster Gateway: "aplanatic"
From Webster's Revised Unabridged Dictionary (1913) (web1913)
Aplanatic \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.
From WordNet (r) 1.7 (wn)
aplanatic
adj : (optics) free from or corrected for spherical aberration;
"an aplanatic mirror"
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