Wide field imaging

New types of prime focus field correctors for Ritchey–Chrétien telescopes are described, which have substantially better imaging than those at present in use. Examples are an improved corrector for the $$\textit{f}/2.7$$ focus of the Cerro Tololo 4-m telescope, and a wider field $$(2^\circ_. 0)$$ corrector for the Anglo–Australian telescope.