Though anti-reflection (AR) coating is basic, essential and like "roots" of coating technology, efforts to improve AR performance by vendors have been disregarded for a long time.
Eventually, it is not easy to find the state-of-the-art AR coating in spite of the long history and importance for astronomical optics.

AR coating should be more notable, because it determines the available wavelengths in the instrument or contributes to reduce the ghost caused by multiple reflection.

Asahi succeeded in coating the outstanding broadband AR coating which covered over 1.5 octaves with R < 0.8% averagely.