A LITTLE-KNOWN 3-LENS CATADIOPTRIC CAMERA BY BERNHARD SCHMIDT

Abstract

The authors investigate a prototype 3-lens f/1 catadioptric camera, built in 1934 by the famous optician Bernhard Schmidt at the Hamburg-Bergedorf Observatory in Germany, where Schmidt worked before his death in 1935. The prototype is in the observatory's collection of Schmidt artifacts, but its nature was not understood before the authors' recent examination. It is an astronomical camera of a form known as 'Buchroeder-Houghton', consisting of a spherical mirror and a 3-element afocal corrector lens placed at the mirror's center of curvature. The design is named for R.A. Buchroeder and J.L. Houghton who independently published this and related forms of wide-field spherical-lens cameras after 1942. Schmidt died before he could publish his own design. The authors disassembled the prototype and measured its optical parameters. These they present together with a transmission test of the corrector lens. The authors also consider the theoretical performance of the design as built, the theory of Houghton cameras, Schmidt's possible path to his invention, and the place of the prototype in his scientific output.