The Schmidt-Väisälä camera is a type of astronomical telescope intended for wide-field (5 to 10 degrees of arc) photographic work. It was designed by Yrjö Väisälä.
Invention and design
Professor Väisälä originally designed an "astronomical camera" similar to Bernhard Schmidt's Schmidt camera, but the design was unpublished. Väisälä did mention it in a lecture notes in 1924 with a footnote: "problematic spherical focal plane". Once Väisälä saw Schmidt's publication, he promptly went ahead and solved the field-flattening problem in Schmidt's design by placing a doubly convex lens slightly in front of the film holder. This resulting system is known as a Schmidt-Väisälä camera or sometimes as Väisälä camera.
This field-flattening solution is not perfect, as images suffer from chromatic aberration with different colors ending up at slightly different places. However the approach is interesting, thinking of modern electronic camera sensors, which definitely cannot be forced into spherical surface shape, nor even manufactured as such.