A super-corrected atmospheric dispersion corrector

The effects of atmospheric dispersion are well known in astrometry and astronomical spectroscopy. To reduce these effects, glass prisms are used. Two different prisms, coupled together, give better corrections. However glass dispersion curves do not match very well the dispersion of the atmosphere and secondary spectrum of the order of 50-100 milliarcseconds (mas) or more will be present. I propose a method to find solutions with residuals less than few parts of 10 milliarcsecond and I show some results.