The Wright telescope is a variation of the Schmidt design which uses a corrector plate at the focus and whose primary mirror is an oblate spheroid. A null test for the mirror is described, which is a modification of the Foucault test, and which makes use of the properties of a particular reference ellipse.
Edgar Everhart, "Null Test for Wright Telescope Mirrors," Appl. Opt. 5, 717-718 (1966)