Schmidt-Väisälä camera
Encyclopedia
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
.
'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, but the design was unpublished.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.
Learning that he lost the inventor status motivated Väisälä to publish his "less than perfect" designs.
Professor Väisälä not only designed the new optics, but also built several implementations of the design after Schmidt's publication.
His two first efforts were experiments to learn how to make the correcting meniscus (a 4th degree polynomial surface).
The third one he built was the Väisälä 500/1031 camera described below, that has been used to find 807 minor planets
and 7 comet
s.
diameter of 500 mm, and a primary mirror focal length of 1031 mm. The spherical primary mirror diameter is 600 mm, and it is on a German-type equatorial mount. It uses a 120-mm diameter doubly convex field flatten lens 3 mm in front of the focal plane, which gives it a 6.7 degree diameter field of view on 120x120 mm film plates giving a scale of 200 arc-seconds per millimeter.
The guide telescopes are 180 mm diameter/2300 mm focal length and 80 mm diameter/1200 mm focal length refracting telescopes.
The telescope was used over some 20 years to find 807 minor planets
and 7 comet
s. Indeed at the time its productivity was similarly compared to the rest of the world's minor planet hunters, and even rivals computerized searches from the 1990s and 2000's. Its surveys, according to one story, may have been intended to detect Earth-impacting asteroids.
For this rather massive photographic survey work, Väisälä developed also a technique of taking two exposures on same plate some 2-3 hours apart and offsetting those images slightly. Any dot that did not have a "pair" was marked for follow-up photos. This method halved the film consumption compared to the method of "blink comparing
", where plates get single exposures, and are compared by rapidly showing first and second exposures to human operator.
The telescope was originally installed at Iso-Heikkilä Observatory
on the outskirts of the city of Turku
, Finland
. When the city grew, together with its lights, the telescope was moved in 1950s to a darker location at Kevola Observatory
, some 35 km east of Turku. The new location is now property of and in care of Turun Ursa Astronomical Association, which is Finland's second oldest amateur astronomy society, and also founded by Väisälä.
This telescope is used rarely (in the 2000s) to take sky photos on 4x5 inch flat plastic film plates. Its guiding telescopes are used mostly to watch stars and planets - e.g. a Pluto
-hunt every spring, for which the guider is barely big enough to allow the human eye to see it under good seeing
conditions.
Yrjö Väisälä
Yrjö Väisälä 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...
.
Invention and design
Professor Väisälä originally designed an "astronomical camera" similar to Bernhard SchmidtBernhard Schmidt
Bernhard Woldemar Schmidt was a German 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...
's Schmidt camera
Schmidt camera
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. Other similar designs are the Wright Camera and Lurie-Houghton telescope....
, 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
Chromatic aberration
In optics, chromatic aberration is a type of distortion in which there is a failure of a lens to focus all colors to the same convergence point. It occurs because lenses have a different refractive index for different wavelengths of light...
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.
Learning that he lost the inventor status motivated Väisälä to publish his "less than perfect" designs.
Professor Väisälä not only designed the new optics, but also built several implementations of the design after Schmidt's publication.
His two first efforts were experiments to learn how to make the correcting meniscus (a 4th degree polynomial surface).
The third one he built was the Väisälä 500/1031 camera described below, that has been used to find 807 minor planets
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
and 7 comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s.
The Väisälä 500/600/1031 camera
This telescope, which saw its first light in 1934, has a corrector plateSchmidt corrector plate
A Schmidt corrector plate is an aspheric lens which is designed to correct the spherical aberration in the spherical primary mirror it is combined with. It was invented by Bernhard Schmidt in 1931, although it may have been independently invented by Finnish astronomer Yrjö Väisälä in 1924...
diameter of 500 mm, and a primary mirror focal length of 1031 mm. The spherical primary mirror diameter is 600 mm, and it is on a German-type equatorial mount. It uses a 120-mm diameter doubly convex field flatten lens 3 mm in front of the focal plane, which gives it a 6.7 degree diameter field of view on 120x120 mm film plates giving a scale of 200 arc-seconds per millimeter.
The guide telescopes are 180 mm diameter/2300 mm focal length and 80 mm diameter/1200 mm focal length refracting telescopes.
The telescope was used over some 20 years to find 807 minor planets
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
and 7 comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s. Indeed at the time its productivity was similarly compared to the rest of the world's minor planet hunters, and even rivals computerized searches from the 1990s and 2000's. Its surveys, according to one story, may have been intended to detect Earth-impacting asteroids.
For this rather massive photographic survey work, Väisälä developed also a technique of taking two exposures on same plate some 2-3 hours apart and offsetting those images slightly. Any dot that did not have a "pair" was marked for follow-up photos. This method halved the film consumption compared to the method of "blink comparing
Blink comparator
A blink comparator was a viewing apparatus used by astronomers to find differences between two photographs of the night sky shot using optical telescopes such as astrographs. It permitted rapidly switching from viewing one photograph to viewing the other, "blinking" back and forth between the two...
", where plates get single exposures, and are compared by rapidly showing first and second exposures to human operator.
The telescope was originally installed at Iso-Heikkilä Observatory
Iso-Heikkilä Observatory
Iso-Heikkilä Observatory is an amateur astronomical observatory in the Iso-Heikkilä district of Turku, Finland. It was operated by the University of Turku from 1937 to 1972 but is now used by a local division of Ursa Astronomical Association.-History:...
on the outskirts of the city of Turku
Turku
Turku is a city situated on the southwest coast of Finland at the mouth of the Aura River. It is located in the region of Finland Proper. It is believed that Turku came into existence during the end of the 13th century which makes it the oldest city in Finland...
, Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
. When the city grew, together with its lights, the telescope was moved in 1950s to a darker location at Kevola Observatory
Kevola Observatory
The Kevola Observatory is located in Kevola in Paimio in South-Western Finland, some 35 km east from the city of Turku. The observatory is currently owned by Turun Ursa ry, a local astronomical association operating in Turku area...
, some 35 km east of Turku. The new location is now property of and in care of Turun Ursa Astronomical Association, which is Finland's second oldest amateur astronomy society, and also founded by Väisälä.
This telescope is used rarely (in the 2000s) to take sky photos on 4x5 inch flat plastic film plates. Its guiding telescopes are used mostly to watch stars and planets - e.g. a Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
-hunt every spring, for which the guider is barely big enough to allow the human eye to see it under good seeing
Astronomical seeing
Astronomical seeing refers to the blurring and twinkling of astronomical objects such as stars caused by turbulent mixing in the Earth's atmosphere varying the optical refractive index...
conditions.
See also
- List of telescope types
- Optical telescopeOptical telescopeAn optical telescope is a telescope which is used to gather and focus light mainly from the visible part of the electromagnetic spectrum for directly viewing a magnified image for making a photograph, or collecting data through electronic image sensors....
- Reflecting telescopeReflecting telescopeA reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
- Schmidt cameraSchmidt cameraA Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations. Other similar designs are the Wright Camera and Lurie-Houghton telescope....
External links
- The Uppsala Väisälä camera from 1941 (310/380/730)
- Turun Ursa Astronomical Association