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63-419: LAMOST is configured as a reflective Schmidt telescope with active optics. There are two mirrors, each made up of a number of 1.1-metre (p-p) hexagonal deformable segments. The first mirror, MA (24 segments, fitting in a 5.72×4.4 m rectangle) is a Schmidt corrector plate in a dome at ground level. The almost-flat mirror MA reflects the light to the south, up a large slanted tunnel (25° above horizontal) to

126-422: A Schmidt corrector plate , located at the center of curvature of 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

189-403: 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 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

252-553: 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Väisälä originally designed an "astronomical camera" similar to Bernhard Schmidt's "Schmidt camera", but the design was unpublished.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

315-409: 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

378-454: 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

441-533: 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

504-498: 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,

567-416: A higher spectral resolution mode where the range is 510–540 and 830–890 nm. Using active optics technique to control its reflecting corrector makes it a unique astronomical instrument in combining large aperture with wide field of view. The available large focal plane may accommodate up to thousands of fibers, by which the collected light of distant and faint celestial objects down to 20.5 magnitude

630-435: 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

693-509: 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

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756-441: A new method of identifying quasars based on their infrared color. An overarching goal of the telescope is to bring Chinese astronomy into the 21st century, taking a leading role in wide-field spectroscopy and in the fields of large-scale and large-sample astronomy and astrophysics. A 2011 conference presentation suggests that there was initially a problem with accuracy of the fiber positioners causing poor throughput, but that this

819-406: A pure Schmidt camera and just behind the prime focus for a Schmidt–Cassegrain . The Schmidt corrector is thicker in the middle and 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

882-400: 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

945-742: 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

1008-419: Is at the top of the left-hand supporting column of the tower, MA is in the left of the two domes at the right of the image (the rightmost, grey dome is an unrelated telescope), and the spectrographs are inside the right-hand column of the tower. Each spectrograph has two 4k×4k CCD cameras, using e2v CCD chips, with 'blue' (370–590 nm) and 'red' (570–900 nm) sides; the telescope can also be used in

1071-541: Is fed into the spectrographs, promising a very high spectrum acquiring rate of ten-thousands of spectra per night. The telescope is to conduct a wide-field survey, called the "LAMOST Experiment for Galactic Understanding and Evolution," or LEGUE. Particular scientific goals of the LAMOST include: It is also hoped that the vast volume of data produced will lead to additional serendipitous discoveries. Early commissioning observations have been able to confirm spectroscopically

1134-545: 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 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,

1197-685: 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

1260-552: 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

1323-520: 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

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1386-762: 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 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

1449-541: The spherical aberration introduced by the spherical primary mirror of 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 ,

1512-464: 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

1575-559: 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

1638-584: 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

1701-409: 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

1764-405: The Schmidt camera. It is now used in several other telescope designs, camera lenses and image projection systems that utilise 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

1827-456: 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 )

1890-723: 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)

1953-421: 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

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2016-646: 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

2079-555: 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

2142-409: 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 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

2205-402: The detector is made curved; in others flat media 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

2268-477: 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

2331-404: 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

2394-407: 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 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

2457-415: 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

2520-406: The larger spherical focusing mirror MB (37 segments, fitting in a 6.67×6.09 m rectangle). This directs light to a focal plane 1.75 metres in diameter corresponding to a five-degree field of view . The focal plane is tiled with 4000 fiber-positioning units, each feeding an optical fiber which transfers light to one of sixteen 250-channel spectrographs below. Looking at the image opposite, MB

2583-404: 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

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2646-532: The most recent data release, DR8, occurred in May 2020. Schmidt corrector plate A Schmidt camera , also referred to as 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),

2709-536: 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

2772-476: 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

2835-425: 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

2898-459: 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

2961-416: 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 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

3024-456: 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

3087-463: 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

3150-421: The tube length can be very long for a wide-field telescope. There are also 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

3213-443: 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 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

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3276-461: 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

3339-401: 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 ,

3402-592: 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

3465-699: 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

3528-408: 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

3591-504: 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

3654-416: 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

3717-525: 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

3780-407: 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

3843-476: 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

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3906-596: Was rectified by adding another calibration step. The same presentation also points out that the telescope's location, only 115 km (71 mi) NW of Beijing , is far from ideal, being in an area with high levels of both atmospheric and light pollution . The telescope has generally been disappointing, with the site receiving only 120 clear nights per year. The first LAMOST data release occurred in June 2013 (DR1). Subsequent data releases occurred in 2014 (DR2), 2015 (DR3), 2016 (DR4), 2017 (DR5), 2018 (DR6), 2019 (DR7), and

3969-587: 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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