Atmospheric dispersion correctors at the Cassegrain focus

The first order aberration theory of an assembly of thin prisms is discussed and the results applied to derive design criteria for atmospheric dispersion correctors located in a converging beam. Two numerical examples are given of Cassegrain focus correctors for a 4.2-m f/11 and a 2.5-m f/15 telescope giving subarcsec imagery over wide spectral ranges and field angles.