Catadioptric system
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A catadioptric optical system is one where
Early catadioptric systems
Catadioptric combinations have been used for many early optical systems. In the 1820s, Augustin-Jean Fresnel developed several catadioptric lighthouse reflector versions of his Fresnel lens.[1] Léon Foucault developed a catadioptric microscope in 1859 to counteract aberrations of using a lens to image objects at high power.[2] In 1876 a French engineer, A. Mangin, invented what has come to be called the Mangin mirror, a concave glass reflector with the silver surface on the rear side of the glass. The two surfaces of the reflector have different radii to correct the aberration of the spherical mirror. Light passes through the glass twice, making the overall system act like a triplet lens.[3] Mangin mirrors were used in searchlights, where they produced a nearly true parallel beam. Many Catadioptric telescopes use negative lenses with a reflective coating on the backside that are referred to as “Mangin mirrors”, although they are not single-element objectives like the original Mangin, and some even predate the Mangin's invention.[4]
Catadioptric telescopes
Catadioptric telescopes are
Catadioptric dialytes
Catadioptric dialytes are the earliest type of catadioptric telescope. They consist of a single-element refracting telescope objective combined with a silver-backed negative lens (similar to a Mangin mirror). The first of these was the Hamiltonian telescope patented by W. F. Hamilton in 1814. The Schupmann medial telescope designed by German optician Ludwig Schupmann near the end of the 19th century placed the catadioptric mirror beyond the focus of the refractor primary and added a third correcting/focusing lens to the system.
Full-aperture correctors
There are several telescope designs that take advantage of placing one or more full-diameter lenses (commonly called a "corrector plate") in front of a spherical primary mirror. These designs take advantage of all the surfaces being "spherically symmetrical"[5] and were originally invented as modifications of mirror based optical systems (reflecting telescopes) to allow them to have an image plane relatively free of coma or astigmatism so they could be used as astrographic cameras. They work by combining a spherical mirror's ability to reflect light back to the same point with a large lens at the front of the system (a corrector) that slightly bends the incoming light, allowing the spherical mirror to image objects at infinity. Some of these designs have been adapted to create compact, long-focal-length catadioptric cassegrains.
Schmidt corrector plate
The
- Popular sub-types
- Schmidt–Cassegrain telescopes are one of the most popular commercial designs on the amateur astronomical market,[6] having been mass-produced since the 1960s. The design replaces the Schmidt Camera film holder with a Cassegrain secondary mirror, making a folded optical path with a long focal length and a narrow field of view.
Meniscus corrector shell
The idea of replacing the complicated Schmidt corrector plate with an easy-to-manufacture full-aperture spherical meniscus lens (a
- Popular sub-types
- collimation).
Houghton corrector lens
The Houghton telescope or Lurie–Houghton telescope is a design that uses a wide compound positive-negative lens over the entire front aperture to correct spherical aberration of the main mirror. If desired, the two corrector elements can be made with the same type of glass, since the Houghton corrector's chromatic aberration is minimal.
The corrector is thicker than a Schmidt-Cassegrain's front corrector, but much thinner than a Maksutov meniscus corrector. All the lens surfaces and the mirror's surface are spheroidal, greatly easing amateur construction.
Sub-aperture correctors
In sub-aperture corrector designs, the corrector elements are usually at the focus of a much larger objective. These elements can be both lenses and mirrors, but since multiple surfaces are involved, achieving good aberration correction in these systems can be very complex.[4] Examples of sub-aperture corrector catadioptric telescopes include the Argunov–Cassegrain telescope, the Klevtsov–Cassegrain telescope and sub-aperture corrector Maksutovs, which use as a "secondary mirror" an optical group consisting of lens elements and sometimes mirrors designed to correct aberration, as well as Jones-Bird Newtonian telescopes, which use a spherical primary mirror combined with a small corrector lens mounted near the focus.[11]
Photographic catadioptric lenses
Various types of catadioptric systems are also used in
Catadioptric lenses do, however, have several drawbacks. The fact that they have a central obstruction means they cannot use an adjustable
Several companies made catadioptric lenses throughout the later part of the 20th century.
Gallery of catadioptric lenses
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500 mm catadioptric lens mounted on a Yashica FX-3
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Minolta AF 500 mm F/8 catadioptric lens mounted on a Sony Alpha 55camera
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Maksutov MC MTO-11CA
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Nikon 500mm f/8 reflex lens
See also
References
- ^ The Encyclopædia Britannica, 1911
- ^ William Tobin, The life and science of Léon Foucault: the man who proved the earth rotates William Tobin, page 214
- ^ Optical design fundamentals for infrared systems By Max J. Riedl
- ^ a b - Vladimir Sacek, telescope-optics.net, Notes on AMATEUR TELESCOPE OPTICS, CATADIOPTRIC TELESCOPES, 10.2.1
- ^ John J. G. Savard, "Miscellaneous Musings"
- ^ Sacek, Vladimir (2006-07-14). "11.5. Schmidt–Cassegrain telescope (SCT)". Telescope Optics. Vladimir Sacek. Retrieved 2009-07-05.
- ^ Lens design fundamentals, by Rudolf Kingslake, page 313 a catadioptric non-monocentric design
- ^ Handbook of Optical Systems, Survey of Optical Instruments, by Herbert Gross, Hannfried Zügge, Fritz Blechinger, Bertram Achtner, page 806
- ^ "Dmitri Maksutov: The Man and His Telescopes By Eduard Trigubov and Yuri Petrunin". Archived from the original on 2012-02-22. Retrieved 2009-08-24.
- ^ patent PDF, DISTRIBUTED BY: National Technical Information Service U. S Archived 2011-06-04 at the Wayback Machine
- ^ 10.1.2. Sub-aperture corrector examples: Single-mirror systems - Jones-Bird
- ^ Astronomy hacks By Robert Bruce Thompson, Barbara Fritchman Thompson, page 59
- ^ R. E. Jacobson, Sidney F. Ray The manual of photography, page 95
External links
- telescope-optics.net, CATADIOPTRIC TELESCOPES
- Learning to love your Mirror Lens - from olympuszuiko.com