Anastigmatic

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 ]