Misplaced Pages

#542457

35-436: LONEOS, in its final configuration, used a 0.6-meter f/1.8 Schmidt telescope , acquired from Ohio Wesleyan University in 1990, and a Lowell-built 16 megapixel CCD detector. This combination of instruments provided a field of view of 2.88 by 2.88 degrees (8.3 square degrees). It had a maximum nightly scan area of about 1,000 square degrees (covered four times). The instrument could cover the entire accessible dark sky in about

70-422: 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

105-403: 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

140-553: 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Väisälä originally designed an "astronomical camera" similar to Bernhard Schmidt's "Schmidt camera", but the design was unpublished.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

175-448: A month. The CCD has detected asteroids as faint as visual magnitude 19.8 but its typical limiting visual magnitude was 19.3. The instrument is located at Lowell Observatory's dark sky site, Anderson Mesa Station , near Flagstaff, Arizona, US. Four computers were used. Two were used for frame reductions, one for telescope pointing control and one for camera control. The camera control software had scripting capability and could control all

210-509: 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

245-406: 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

280-634: A slash. The second number represents the number of discoveries larger than one kilometer. The column labeled "Asteroid Observations" is the number of observations sent to the Minor Planet Center. Each asteroid was typically observed four times (once per frame) each night. A complete list of LONEOS NEO observations can be found at the NeoDys web site. The LONEOS frame archive provides a data set with wide spatial and temporal sky coverage. Other investigators have used these characteristics to produce

315-549: A typical main-belt asteroid. Human examination was required because most putative NEO detections were not real but some kind of imaging artifact. All asteroid positions were converted to equatorial coordinates . Various USNO star catalogs were used for this conversion until 2007. Then the Sloan Digital Sky Survey catalog was used, along with supplemental information from the Carlsberg Catalog and

350-742: 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

385-545: 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,

SECTION 10

#1732783455543

420-493: The 2MASS catalog. Asteroid brightness was converted to standard visual magnitude . These data, along with the time of the observations, were sent to the Minor Planet Center (MPC) from which they were distributed to the scientific community. Potential near-Earth objects were handled expeditiously so that other observers could locate the asteroid on the same night and make further observations. Telescope operation

455-762: 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

490-541: 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 ,

525-639: 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

560-405: 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

595-514: 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 Too Many Requests If you report this error to the Wikimedia System Administrators, please include

630-723: 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)

665-409: 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

700-402: 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

735-404: 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

SECTION 20

#1732783455543

770-407: 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

805-502: The following research papers and presentations. Lowell staff: Collaborators: Schmidt telescope 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),

840-459: 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

875-420: The other computers. Asteroids were found by obtaining four pictures (frames) of the same region of sky, each frame temporally separated by 15 to 30 minutes. The set of four frames were then submitted to reduction software which located all star-like sources on the frame and identified sources that moved with asteroid-like motion. The observer visually examined all asteroid detections that had motion different from

910-416: 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

945-642: The period of LONEOS operation, several other NASA funded NEO searches were underway (number of discoveries in parentheses): Amateur observers made a significant contribution during this time with independent NEO discoveries and by performing follow-up observations of recent discoveries made by the NASA sponsored surveys. The table below lists the number of discoveries made by LONEOS each year of operation. Asteroids thought to be larger than one kilometer in diameter were used as benchmarks in assessing survey completeness. Hence, some table elements have two numbers separated by

980-463: 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

1015-421: 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

1050-443: 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

1085-699: 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

Lowell Observatory Near-Earth-Object Search - Misplaced Pages Continue

1120-509: Was automated to the extent that the survey could be run all night without observer intervention. However, the telescope was seldom operated in the automatic mode because an observer was required to reduce data promptly and to correct any malfunctions that might have occurred. As of 2017, LONEOS is credited by the Minor Planet Center with the discovery of 22,077 minor planets between 1998 and 2008. The discoveries include main-belt asteroids , near-Earth Objects (NEO) and Mars-crossers . During

1155-525: 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

1190-476: 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

1225-587: 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

#542457