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Yrjö Väisälä (6 September 1891〔The birth date is a Gregorian calendar date. Although Finland was part of the Russian Empire at the time and Russia used the Julian calendar until 1918, the Gregorian calendar continued in official use in Finland because Finland had been part of Sweden when Sweden had converted to the Gregorian calendar in 1753.〕 – 21 July 1971) was a Finnish astronomer and physicist. His main contributions were in the field of optics, but he was also very active in geodetics, astronomy and optical metrology. He had even an affectionate nickname of ''Wizard of Tuorla'' (Observatory/Optics laboratory), and there is a book with the same title in Finnish describing his works. His brothers were mathematician Kalle Väisälä and meteorologist Vilho Väisälä. Väisälä was also a fervent supporter of Esperanto, presiding the ''Internacia Scienca Asocio Esperantista'' ("International Association of Esperanto Scientists") in 1968.〔(Esperanta Finnlando numero 1/1968 )〕 == Optician == He developed several methods for measuring the quality of optical elements, as well as a lot of practical methods of manufacturing said elements. This allowed the construction of some of the earliest high-quality Schmidt cameras, in particular a "field-flattened" version known as Schmidt-Väisälä camera. Contemporary to Bernhard Schmidt's design, but unpublished was also Prof. Yrjö Väisälä's identical design which he had mentioned in lecture notes in 1924 with a footnote: "problematic spherical focal surface". Once he saw Schmidt's publication, he promptly went ahead and "solved" the field flattening problem by placing a doubly convex lens slightly in front of the film holder – back in the 1930s, astronomical films were glass plates ''(also see photographic plates)''. The resulting system is known as the Schmidt-Väisälä camera or sometimes as the ''Väisälä camera''. (This solution is not perfect, as images of different colour end up at slightly different places.) Prof. Väisälä made a small test unit of 7 mirrors in a mosaic on stiff background steel frame, however it proved to be impossible to stabilize as "just adjust and forget" structure, and next time anybody tried it, was with active controls on Multiple Mirror Telescope. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Yrjö Väisälä」の詳細全文を読む スポンサード リンク
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