Telescope Ritchey-Christian

In Astronomy, the telescope Ritchey-Christian is a Télescope of the type particular Cassegrain, conceived to eliminate the Aberration called coma. This type of telescope thus provides a relatively broad observation field compared with a more conventional design. In the Telescope Ritchey-Christian, the primary education Mirror and the secondary Miroir is hyperbolic. He was invented at the beginning of the Années 1910 by the American astronomer George Willis Ritchey (1864 – 1945) and the French astronomer Christian Henri (1879 – 1956). Ritchey built the first telescope Ritchey-Christian successfully, of a diameter of 0,5 m, in 1927. The second specimen was a model of 1 meter built by Ritchey for the naval observatory of the United States.

Design

The design of the Ritchey-Christian type is of coma to the 3rd order and free from Spherical aberration, although she suffers from coma to the 5th order, severe a Astigmatisme with the great angles and from a rather important curve of field. When it is focused halfway of the focal plane sagittal and tangential, the star S seem circles, returning this type of telescope adapted well to the observation with broad field and the Astrophotographie. As on the other telescopes of the Cassegrain type, the telescope Ritchey-Christian has a very short optical tube and a compact design for a focal length given. It offers optical good performances out-axis, but there remains relatively rare because of the high cost of manufacture of the primary education mirror. The design Ritchey-Christian generally meets on the high performance professional telescopes.

The curves of the two mirrors in the design Ritchey-Christian are calculated by the following relations:

C_1 = \ frac {(B - F)}{2DF}

C_2 = \ frac {(B + D - F)}{2DB}

where:

  • C1 and C2 is the Coefficients of deformation of Schwarzschild of the mirrors primary education and secondary, respectively,
  • F is the effective focal length complete system,
  • B is back focal length, equal to the distance between the secondary mirror and the hearth,
  • D is the distance between the two mirrors.

A suitable choice of B, D and of F makes it possible to obtain all the configurations of telescope

The hyperbolic curves are difficult to check with the equipment used by the artisanal manufacturers amateurs or manufacturers. However, the manufacturers of professional optics and the important groups of research check their mirrors with Interféromètre S. a Ritchey-Christian thus does not ask for an additional equipment, for a broad profit in performances.

List partial of large telescopes Ritchey-Christian

  • the two telescopes of 10 m of the observatory Keck
  • the four telescopes of 8,2 m of the Broad Very currently Telescopes with the Chile
  • the two telescopes of 8 m of the Observatoire Gemini
  • the Gran Telescopio Canarias of 10,4 m to the Observatoire of the Castling of los Muchachos
  • the telescope Subaru of 8,2 m to the Observatoire of Mauna Kea
  • the Space telescope Hubble of 2,4 m in orbit around the Earth
  • the infra-red Space telescope Herschel of 3,5 m

Ritchey proposed that the Télescope Hauls of 200 inches (5 m) of the Mont Palomar is a Ritchey-Christian. Its design would have provided clearer images on a broader observation field. But Richtey and Hale were scrambled. Haul refused to adopt the new design with its complex curves and Ritchey left the project (being given the great times of construction, Hale could be forgiven to have wanted to avoid a risk). The proposal of Ritchey will be validated later, because the Hale telescope was the last telescope of big size to have a parabolic primary education mirror.

See also

  • Telescope of the type Cassegrain
  • Telescope Maksutov
  • Telescope of Newton
  • Telescope Schmidt-Cassegrain
  • List of the largest telescopes
  • List of the astronomical observatories

References

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