A Quasi-Aplanatic Refractive Pair for Correcting Astigmatism in Ritchey-Chrétien Telescopes

A quasi-aplanatic two-lens design is proposed to correct astigmatism in Ritchey-Chr´etien (RC) telescopes at different spectral bands. This pair of lenses is designed analytically so that it can be used in existing RC telescopes without any modification of the mirror’s shapes while introducing only a small amount of coma. The field of view (FoV) is consequently increased due to the astigmatism being corrected by the two lenses and due to the final image being flattened. Astigmatism can be corrected individually for each spectral band by merely changing the distance between the two lenses.