a. 消像散的

[医] 无散光的

Anastigmatic \An*as`tig*mat"ic\, a. [Pref. an-not + astigmatic.]
(Optics)
Not astigmatic; free of astigmatism; -- pertaining to a lens
or lens system, and used especially of a lens system which
consists of a converging lens and a diverging lens of equal
and opposite astigmatism but different focal lengths, and
sensibly free from astigmatism.
[Webster 1913 Suppl. + WordNet 1.5]