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58-460: The observatory established a 1-meter Schmidt telescope in 1963, which is a large size for this type of telescope designed to give a wide field of view. The observatory was the result of a donation in 1944 from Nils Tamm, an artist who had studied astronomy in his youth under Nils Christoffer Dunér and Östen Bergstrand in Uppsala and remained an avid amateur astronomer throughout his life. Through

116-546: A design was used to construct a working 1/8-scale model of the Palomar Schmidt, with a 5° field. The retronym "lensless Schmidt" has been given to this configuration. Yrjö Väisälä originally designed an "astronomical camera" similar to Bernhard Schmidt's "Schmidt camera", but the design was unpublished. Väisälä did mention it in lecture notes in 1924 with a footnote: "problematic spherical focal plane". Once Väisälä saw Schmidt's publication, he promptly went ahead and solved

174-409: A diaphragm at a particular location, and a "correction plate") into a simple catadioptric system, based on reasoning from first principles, was epoch making. In particular, the "correction plate" was like nothing ever seen before in telescope design. After Schmidt a flood of new catadioptric designs appeared in the subsequent decades. Schmidt built his first "Schmidtspiegel" (which came to be known as

232-449: A facility located outside Hamburg in the countryside near the village of Bergedorf . Schorr had become interested in Schmidt's horizontal mirror and coelostat telescope and ordered one to be built for his observatory. After the war when Schmidt's economic situation became increasingly difficult, Schmidt began making overtures to Schorr for some kind of work at the observatory. Schorr had only

290-524: A family visit and to scout out opportunities in optics, as Estonia had become an independent republic after World War I. Nothing came of these efforts, and by 1927 Schmidt's prospects were so poor that he accepted Schorr's offer. He began to establish a workshop in the basement of the Main Service Building at the observatory and to repair the horizontal telescope. During 1927 and 1929, Schmidt participated in two solar eclipse expeditions mounted by

348-489: A field more than 15 degrees in diameter, making it possible to image large swathes of sky with short exposures (on the order of a few minutes versus an hour or more with a conventional reflector). His first camera had an aperture of about 360 mm or 14.5" in diameter, and a focal ratio of f/1.75. It is now housed in a museum at the Hamburg Observatory . Schmidt's combining of diverse optical elements (a special mirror,

406-435: A little to offer: Schmidt could come to Bergedorf and lodge for free; there was repair work to do on the horizontal telescope, for which he would be paid a small fee. This was in 1926. For a time Schmidt did not accept. He had a number of patents to his credit, one of which involved using a wind-driven propeller to power boats forward. Schmidt hoped to turn this invention into something profitable. He also went back to Estonia for

464-494: A multiple axis mount allowing it to follow satellites in the sky – were used by the Smithsonian Astrophysical Observatory to track artificial satellites from June 1958 until the mid-1970s. The Mersenne–Schmidt camera consists of a concave paraboloidal primary mirror, a convex spherical secondary mirror, and a concave spherical tertiary mirror. The first two mirrors (a Mersenne configuration) perform

522-411: A spherical primary mirror. Schmidt corrector plates work because they are aspheric lenses with spherical aberration that is equal to but opposite of the spherical primary mirrors they are placed in front of. They are placed at the center of curvature " C " of the mirrors for a pure Schmidt camera and just behind the prime focus for a Schmidt–Cassegrain . The Schmidt corrector is thicker in the middle and

580-434: A vacuum pan with the correct shape of the curve pre-shaped into the bottom of the pan, called a "master block". The upper exposed surface is then polished flat creating a corrector with the correct shape once the vacuum is released. This removes the need to have to hold a shape by applying an exact vacuum and allows for the mass production of corrector plates of the same exact shape. The technical difficulties associated with

638-400: A way to photograph large swathes of the sky quickly for the purpose of surveying the visible contents of the universe and seeing large-scale structures. Ordinary telescopes up till Schmidt's time showed narrow fields of view, typically measuring 1 or 2 degrees in diameter. Surveying the whole sky with such telescopes required an enormous investment of time and resources over years and (because of

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696-708: Is also a Schmidt camera. The Schmidt telescope of the Karl Schwarzschild Observatory is the largest Schmidt camera of the world. A Schmidt telescope was at the heart of the Hipparcos (1989–1993) satellite from the European Space Agency . This was used in the Hipparcos Survey which mapped the distances of more than a million stars with unprecedented accuracy: it included 99% of all stars up to magnitude 11. The spherical mirror used in this telescope

754-429: Is mechanically conformed to the shape of the focal plane through the use of retaining clips or bolts, or by the application of a vacuum . A field flattener , in its simplest form a planoconvex lens in front of the film plate or detector, is sometimes used. Since the corrector plate is at the center of curvature of the primary mirror in this design the tube length can be very long for a wide-field telescope. There are also

812-496: Is rarely used today. Holding the shape by constant vacuum is difficult and errors in the o-ring seal and even contamination behind the plate could induce optical errors. The glass plate could also break if bent enough to generate a curve for telescopes of focal ratio f/2.5 or faster. Also, for fast focal ratios, the curve obtained is not sufficiently exact and requires additional hand correction. A third method, invented in 1970 for Celestron by Tom Johnson and John O'rourke, uses

870-502: Is the Kepler space telescope exoplanet finder. Other related designs are the Wright camera and Lurie–Houghton telescope . The Schmidt camera was invented by Estonian-German optician Bernhard Schmidt in 1930. Its optical components are an easy-to-make spherical primary mirror , and an aspherical correcting lens , known as a Schmidt corrector plate , located at the center of curvature of

928-665: The Chalmers University of Technology , but soon thereafter switched to the University of Mittweida in the Kingdom of Saxony to further his education. During this period his interest in astronomy and optics increased. In Mittweida he had hoped to study with Dr. Karl Strehl, a noted optical theorist. Strehl, however, had recently departed. Gradually, Schmidt found his true calling, namely the grinding and polishing of highly precise optics for astronomical applications. He seems to have begun

986-535: The Mount Wilson Observatory in the United States, the Schmidt telescope idea took off. An 18" Schmidt was produced in 1936 and then twelve years later, the famous 48" (122 cm) Samuel Oschin telescope Schmidt-telescope was built at Mount Palomar Observatory . This last telescope produced a flood of new observations and information. Subsequently at Bergedorf in 1955 a large, well-constructed Schmidt

1044-507: The Potsdam Astrophysical Observatory. As his business increased, he hired several assistants, two of whom have left valuable accounts of Schmidt's working methods. Schmidt also bought an automobile, a rare luxury then, and employed a friend as chauffeur. Using a long focus horizontal mirror and a plane coelostat, both of his own manufacture, he took impressive photos of the sun, moon and major planets. World War I brought

1102-588: The Schmidt or Schmidt–Cassegrain telescope designs. It was invented by Bernhard Schmidt in 1931, although it may have been independently invented by Finnish astronomer Yrjö Väisälä in 1924 (sometimes called the Schmidt–Väisälä camera as a result). Schmidt originally introduced it as part of a wide-field photographic catadioptric telescope , the Schmidt camera. It is now used in several other telescope designs, camera lenses and image projection systems that utilise

1160-647: The Schmidt telescope , is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations . The design was invented by Bernhard Schmidt in 1930. Some notable examples are the Samuel Oschin telescope (formerly Palomar Schmidt), the UK Schmidt Telescope and the ESO Schmidt; these provided the major source of all-sky photographic imaging from 1950 until 2000, when electronic detectors took over. A recent example

1218-464: The " Schmidt corrector plate ") at the same center of curvature as the apertured diaphragm. This aspheric lens has a complex curve that is convex near its middle and concave near its periphery that creates the opposite spherical aberration of the spherical mirror it is paired with, canceling out the mirror's spherical aberration. In this way, very neatly and simply he could construct a large camera of f/1.75 or even faster, that would give sharp images across

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1276-544: The Hamburg Observatory, the first to northern Sweden and the second to the Philippines . It was during this second trip that Schmidt announced to his companion, the astronomer Walter Baade , the most important invention of Schmidt's lifetime, indeed an invention that revolutionized astronomy and optical design in the second half of the 20th century, namely his wide-angle reflective camera. Astronomers had long wished for

1334-409: The Schmidt camera) in 1930, a breakthrough which caused a sensation around the world. He employed a very clever method (the so-called "vacuum pan" method) to make the difficult "corrector plate", so that the system gave superb images. The vacuum pan involved carefully warping a parallel glass plate under partial vacuum into a slight sagging curve and then polishing the upper curve flat. After release of

1392-456: The Schmidt design directing light through a hole in the primary mirror creates a Schmidt–Cassegrain telescope . The last two designs are popular with telescope manufacturers because they are compact and use simple spherical optics. A short list of notable and/or large aperture Schmidt cameras. Bernhard Schmidt Bernhard Woldemar Schmidt (11 April [ O.S. 30 March] 1879, Nargen, Estonia – 1 December 1935, Hamburg )

1450-680: The UK Science Research Council with a 1.2 meter Schmidt telescope at Siding Spring Observatory engaged in a collaborative sky survey to complement the first Palomar Sky Survey, but focusing on the southern hemisphere. The technical improvements developed during this survey encouraged the development of the Second Palomar Observatory Sky Survey (POSS II). The telescope used in the Lowell Observatory Near-Earth-Object Search (LONEOS)

1508-421: The age of 56. A postmortem revealed that he was suffering from a lung infection. In book 2 of "I Wish I'd Been There, European History c.2008 by American Historical Publications, Freeman Dyson wrote, "He (Schmidt) bought a sufficient supply of cognac and quietly drank himself to death." Schmidt did not marry and had no children. Soon after his death, through the advocacy of Walter Baade when he arrived at

1566-627: The beginning of the Great Depression . No orders came in and he remained dependent on Schorr and Bergedorf for a modest income from occasional jobs till the end of his life. He produced a larger camera in 1934 and reground the 60 cm Bergedorf-Steinheil photographic refractor as well. Schmidt fell ill at the end of November 1935 after a business trip to Leiden in the Netherlands . Despite attempts at treatment, he died on 1 December 1935 in Hamburg at

1624-548: The boom to an end. Schmidt was arrested as an enemy-alien, as Estonia belonged to the Russian Empire , and was sent to an internment camp for about six months. After his release, he remained under police control and some of his suspicious-looking astronomical equipment was confiscated. He attempted to continue his business, but as the war dragged on and turned to defeat for Germany, the economy became grim and scientists had no money for astronomy. The situation did not improve after

1682-453: The corrector by grinding and polishing the aspherical shape into a flat glass blank using specially shaped and sized tools. This method requires a high degree of skill and training on the part of the optical engineer creating the corrector. Schmidt himself worked out a second, more elegant, scheme for producing the complex figure needed for the correcting plate. A thin glass disk with a perfectly polished accurate flat surface on both sides

1740-419: The drawbacks of having the obstruction of the film holder or detector mounted at the focus halfway up the tube assembly, a small amount of light is blocked and there is a loss in contrast in the image due to diffraction effects of the obstruction and its support structure. A Schmidt corrector plate is an aspheric lens which corrects the spherical aberration introduced by the spherical primary mirror of

1798-451: The edge. This corrects the light paths so light reflected from the outer part of the mirror and light reflected from the inner portion of the mirror is brought to the same common focus " F ". The Schmidt corrector only corrects for spherical aberration. It does not change the focal length of the system. Schmidt corrector plates can be manufactured in many ways. The most basic method, called the "classical approach", involves directly figuring

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1856-472: The excellence of Schmidt's mirrors for their researches. Between 1904 and 1914, Schmidt's business boomed and he acquired an immense reputation in Germany. Not only did he produce some of the most difficult and precise mirrors ever attempted up to that time, but he was entrusted with correcting and improving lenses originally supplied by famous optical houses, for example the 50 cm Steinheil visual refractor at

1914-404: 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: Schmidt–Väisälä camera or sometimes as Väisälä camera . In 1940, James Baker of Harvard University modified the Schmidt camera design to include a convex secondary mirror, which reflected light back toward the primary. The photographic plate

1972-415: The grinding of mirrors sometime around 1901, and thereafter began to sell some of his products to amateur astronomers. By March 1904, he had made so much progress in his new endeavor that after finishing his studies, he was soon in contact with professionals at the major observatories in Germany. His business rapidly took off when noted astronomers such as Hermann Carl Vogel , and Karl Schwarzschild realized

2030-404: The middle of their fields of view, quickly lost their definition away from the field center. Star images became bloated and comet-shaped, with the head of the "comet" pointing to the middle of the photographic field. This bloating results mainly from the optical aberrations (i.e. errors) called "coma" and "astigmatism". Before Schmidt it was impossible to build a large, fast reflector telescope which

2088-536: The narrow views) tended to miss large structures. It was possible to see large swathes with small camera lenses, but then faint (and hence far away) objects would remain invisible. What was needed was large aperture cameras possessing wide fields of good imaging properties ("definition"), and fast focal ratios to decrease exposure times. Unfortunately, the only large aperture wide-field telescopes before Schmidt were ordinary reflecting telescopes of short focal ratio (about f/3), and these presented images which while sharp at

2146-471: The night sky and constellations. One misadventure proved tragic and marked Schmidt for the rest of his life. When he was 15 years old, he experimented with gunpowder . He packed an iron pipe with a charge, but through a mistake with the fuse the pipe exploded, and he lost the thumb and index finger of his right hand. Despite his mother's attempts to clean and bandage the wounds, surgeons in Tallinn later amputated

2204-425: The normal paraboloidal mirror of a reflector telescope) and a smaller apertured diaphragm placed at the center of curvature of the mirror, he could at a stroke eliminate coma and astigmatism. He would be left, however, with spherical aberration which is just as damaging to image sharpness. Schmidt realized that he could eliminate the spherical aberration by placing a thin, very weakly curved aspheric lens (now called

2262-459: The object. Starting in the early 1970s, Celestron marketed an 8-inch Schmidt camera. The camera was focused in the factory and was made of materials with low expansion coefficients so it would never need to be focused in the field. Early models required the photographer to cut and develop individual frames of 35 mm film, as the film holder could only hold one frame of film. About 300 Celestron Schmidt cameras were produced. The Schmidt system

2320-406: The pan until a particular negative pressure had been achieved. This caused the glass plate to warp slightly. The exposed upper surface of the glass was then ground and polished spherical. When the vacuum was released, the lower surface of the plate returned to its original flat form while the upper surface had the aspheric figure needed for a Schmidt corrector plate. Schmidt's vacuum figuring method

2378-456: The port of Reval. With his younger brother August Fredrik, Bernhard Schmidt engaged in many childhood adventures on the island. He was an extremely inquisitive, inventive, and imaginative young person and adult. For example, when young he built his own camera from a purchased lens and old concertina bellows and succeeded in photographing his local surroundings and various family members, and even sold some of his photos. He also became fascinated with

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2436-405: The primary mirror. The film or other detector is placed inside the camera, at the prime focus. The design is noted for allowing very fast focal ratios , while controlling coma and astigmatism . Schmidt cameras have very strongly curved focal planes , thus requiring that the film, plate, or other detector be correspondingly curved. In some cases the detector is made curved; in others flat media

2494-834: The production of Schmidt corrector plates led some designers, such as Dmitri Dmitrievich Maksutov and Albert Bouwers , to come up with alternative designs using more conventional meniscus corrector lenses. Because of its wide field of view, the Schmidt camera is typically used as a survey instrument, for research programs in which a large amount of sky must be covered. These include astronomical surveys , comet and asteroid searches, and nova patrols. In addition, Schmidt cameras and derivative designs are frequently used for tracking artificial Earth satellites . The first relatively large Schmidt telescopes were built at Hamburg Observatory and Palomar Observatory shortly before World War II . Between 1945 and 1980, about eight more large (1 meter or larger) Schmidt telescopes were built around

2552-457: The same function of the correcting plate of the conventional Schmidt. This form was invented by Paul in 1935. A later paper by Baker introduced the Paul-Baker design, a similar configuration but with a flat focal plane. The addition of a flat secondary mirror at 45° to the optical axis of the Schmidt design creates a Schmidt–Newtonian telescope . The addition of a convex secondary mirror to

2610-457: The vacuum, the lens would spring back into the "Schmidt shape" needed for the camera. No one had ever made a lens in this way before. Schmidt published a brief account (in German ) of his invention in professional publications, and offered to build his cameras for professional observatories. Unfortunately, his publicity was too little and his design was too novel. Moreover, the invention coincided with

2668-401: The war because of the political turmoil in Germany and the need to pay war reparations. Inflation galloped out of control in 1923 and many people lost their entire savings. By the mid-1920s, Schmidt's business was ruined and he had to liquidate his remaining equipment as junk. From 1916 onward Schmidt had been in contact with Professor Richard Schorr , the director of the Hamburg Observatory ,

2726-580: The whole hand. This event appears to have deepened his reserve and introspection, qualities well noted by his contemporaries in later life. In spite of his loss, Schmidt was soon experimenting and inventing again. He also took more photos and became adept at developing and printing them. In 1895 he moved to Tallinn, and for a time worked at retouching photographs. Later he worked for the Volta Electrical Motor Works and became skilled in drafting. In 1901 he went to Gothenburg , Sweden , to study at

2784-402: The work of professor Åke Wallenquist and professor Gunnar Malmquist at the observatory in Uppsala, the new observatory was fitted out with a large Schmidt telescope (100/135/300 cm) in 1963. Wallenquist became the first director of the observatory (1948–1970) and was succeeded by Tarmo Oja (1970–1999) and later Claes-Ingvar Lagerkvist (1999–2007). The asteroid 3331 Kvistaberg ,

2842-666: The world. One particularly famous and productive Schmidt camera is the Oschin Schmidt Telescope at Palomar Observatory , completed in 1948. This instrument was used in the National Geographic Society – Palomar Observatory Sky Survey (POSS, 1958), the POSS-II survey, the Palomar-Leiden (asteroid) Surveys, and other projects. The European Southern Observatory with a 1-meter Schmidt telescope at La Silla and

2900-408: Was an Estonian optician . In 1930 he invented the Schmidt telescope , which corrected for the optical errors of spherical aberration , coma, and astigmatism, making possible for the first time the construction of very large, wide-angled reflective cameras of short exposure time for astronomical research. Schmidt was the son of Carl Constantin and Marie Helene Christine ( née Rosen) Schmidt. He

2958-504: Was born and grew up on the island of Nargen (Naissaar), off the coast of Reval (Tallinn), Estonia , then part of the Russian Empire . The inhabitants of this island, mainly Estonian Swedes , generally spoke Swedish or Estonian , but the Schmidt family also spoke German . Bernhard was the oldest of six children, three boys (one of whom died in infancy) and three girls. Naissaar was a small, rural island whose population mainly supported themselves through fishing and piloting ships into

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3016-416: Was dedicated. The 2-metre Schmidt telescope of the Karl Schwarzschild Observatory was built later and remains the largest Schmidt camera in the world, although more technologically advanced versions have since been produced. The Bergedorf Schmidt was moved to Calar Alto Observatory in 1976. Schmidt is also the protagonist of the biographic novel Vastutuulelaev: Bernhard Schmidti romaan ( Sailing Against

3074-518: Was extremely accurate; if scaled up to the size of the Atlantic Ocean , bumps on its surface would be about 10 cm high. The Kepler photometer , mounted on NASA's Kepler space telescope (2009–2018), is the largest Schmidt camera launched into space. In 1977 at Yerkes Observatory , a small Schmidt telescope was used to derive an accurate optical position for the planetary nebula NGC 7027 to allow comparison between photographs and radio maps of

3132-481: Was named for the astronomical observatory, where hundreds of minor planets had been discovered with the Schmidt telescope between 1975 and 2005. Around 2004, Uppsala University decided to discontinue active research at the observatory. The property was sold to the municipality of Upplands-Bro, where Kvistaberg is situated. The domes and telescopes are now part of a museum, which was inaugurated in 2009. Schmidt telescope A Schmidt camera , also referred to as

3190-407: Was not plagued by these errors. Schmidt was well aware of this and had been pondering possible solutions during the late 1920s. According to Baade, he had abandoned at least one solution already, when finally he hit upon his ultimate design, which involved a novel, indeed bold departure from traditional optical designs. Schmidt realized that by employing a large spherically shaped mirror (instead of

3248-406: Was placed on a heavy rigid metal pan. The top surface of the pan around the edge of the glass disk was ground at a precise angle or bevel based on the coefficient of elasticity of the particular type of glass that was being used. The glass plate was sealed to the ground edge of the pan. Then a vacuum pump was used to exhaust the air between the pan and glass through a small hole in the center of

3306-472: Was popular, used in reverse, for television projection systems, notably the Advent design by Henry Kloss . Large Schmidt projectors were used in theaters, but systems as small as 8 inches were made for home use and other small venues. In the 1930s, Schmidt noted that the corrector plate could be replaced with a simple aperture at the mirror's center of curvature for a slow (numerically high f-ratio) camera. Such

3364-574: Was then installed near the primary, facing the sky. This variant is called the Baker-Schmidt camera. The Baker–Nunn design, by Baker and Joseph Nunn , replaces the Baker-Schmidt camera's corrector plate with a small triplet corrector lens closer to the focus of the camera. It used a 55 mm wide film derived from the Cinemascope 55 motion picture process. A dozen f/0.75 Baker-Nunn cameras with 20-inch apertures – each weighing 3.5 tons including

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