Schmidt’s 1934 three lens replacement for an aspheric plate, and some new variations

Several designs are shown that are alternatives to Bernhard Schmidt’s largely unknown 1934 three lens corrector replacement for an aspheric plate in his famous telescope. OCIS codes: (220.2740) Geometric optical design; (220.3620) Lens system design A fascinating story from lens design history was chronicled in a 2013 article [1], about how Bernhard Schmidt designed and built in 1934 a three lens replacement, shown here, for the aspheric plate in an f/1.0 Schmidt camera. Fig. 1 Schmidt’s 1934 system Fig. 2 Three lens corrector for a spherical mirror Schmidt’s triplet corrector design was completely symmetrical but better performance is achieved when radii symmetry is abandoned and the lens airspaces are increased a little, as shown in Figure 2. Schmidt died before he could publish his results. 10 years later James Houghton’s 1944 US patent 2,350,112 was the first published version of this catadioptric design and his name has been associated with it ever since. Later Buchroeder [2], published some designs of this type in 1972. The image is curved and there are versions where an extra lens is added right near the image to get a flat field. The original systems used a curved film platen at the image. It turns out that there are a variety of three lens correctors possible in addition to the type that Schmidt showed. Fig. 3 Alternate design with good correction Fig. 4 Baker SuperSchmidt with aspheric plate Figure 3 shows an alternate f/1.0 three lens design that has somewhat better performance than the Figure 2 design. International Optical Design Conference 2017, edited by Peter P. Clark, Julius A. Muschaweck, Richard N. Pfisterer, John R. Rogers, Proc. of SPIE-OSA Vol. 10590, 1059015 · © 2017 SPIE CCC code: 0277-786X/17/$18 · doi: 10.1117/12.2302386 Proc. of SPIE-OSA/ Vol. 1059