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| Headquarters | Japan |
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| Website | vixen |
Vixen is a Japanese company that makes telescopes, binoculars, spotting scopes and accessories for their products.
Among many other more mainstream products they have created two unusual varieties of catadioptric telescopes with an open tube design instead of the full-aperture corrector plate of the Schmidt–Cassegrain and most Maksutov–Cassegrain designs.
This design is based on the Maksutov–Cassegrain. It provides correction of aberrations via a two-element meniscus-shaped corrector lens in front of the secondary mirror. This design was originally envisaged by G. I. Popov with a practical implementation by Yu. A. Klevtsov. It is produced with apertures of 8, 10.25 and 13 inches. The 8-inch model employs a refractor style rack and pinion focuser, while in the larger designs the primary mirror is moved as in most other small to medium-sized Cassegrain designs.
Vixen produces an 8-inch aperture-modified Cassegrain design (VC200L) they refer to as a VISAC (Vixen Sixth-Order Aspheric Cassegrain) that is based on a Cassegrain design with a primary mirror that is "sixth order aspheric" – somewhat like a hyperbolic mirror but able to be manufactured using mass-production techniques. To compensate for the aberrations the mirror design introduces, Vixen adds a "field corrector lens" – actually a three-element corrector in the draw tube of the focuser which also reduces field curvature for wide field applications. The design results in an image that is free of coma and astigmatism. These characteristics have led to the VISAC being referred to as a "Poor man's Ritchey–Chrétien". In fact, given that it has no astigmatism and field curvature, it performs better than a true RC. There is the downside of the potential for chromatic aberration due to the refractive elements, but it is hardly noticeable.
This particular design is also unusual in that it is a Cassegrain design but has a fixed primary and refractor-style rack-and-pinion focuser which removes the image shift issues seen with other catadioptric designs.
These features together make for a telescope that is very well suited to astrophotography either at the native f/9 or using the optional focal reducer at around f/6.3.
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The Cooke triplet is a photographic lens designed and patented in 1893 by Dennis Taylor who was employed as chief engineer by T. Cooke & Sons of York. It was the first lens system that allowed elimination of most of the optical distortion or aberration at the outer edge of the image.
A Ritchey–Chrétien telescope is a specialized variant of the Cassegrain telescope that has a hyperbolic primary mirror and a hyperbolic secondary mirror designed to eliminate off-axis optical errors (coma). The RCT has a wider field of view free of optical errors compared to a more traditional reflecting telescope configuration. Since the mid 20th century, a majority of large professional research telescopes have been Ritchey–Chrétien configurations; some well-known examples are the Hubble Space Telescope, the Keck telescopes and the ESO Very Large Telescope.
In optics, spherical aberration (SA) is a type of aberration found in optical systems that have elements with spherical surfaces. Lenses and curved mirrors are prime examples, because this shape is easier to manufacture. Light rays that strike a spherical surface off-centre are refracted or reflected more or less than those that strike close to the centre. This deviation reduces the quality of images produced by optical systems. The effect of spherical aberration was first identified by Ibn al-Haytham who discussed it in his work Kitāb al-Manāẓir.
A reflecting telescope is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century by Isaac Newton as an alternative to the refracting telescope which, at that time, was a design that suffered from severe chromatic aberration. Although reflecting telescopes produce other types of optical aberrations, it is a design that allows for very large diameter objectives. Almost all of the major telescopes used in astronomy research are reflectors. Many variant forms are in use and some employ extra optical elements to improve image quality or place the image in a mechanically advantageous position. Since reflecting telescopes use mirrors, the design is sometimes referred to as a catoptric telescope.
The Newtonian telescope, also called the Newtonian reflector or just a Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton, using a concave primary mirror and a flat diagonal secondary mirror. Newton's first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope. The Newtonian telescope's simple design has made it very popular with amateur telescope makers.
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.
A catadioptric optical system is one where refraction and reflection are combined in an optical system, usually via lenses (dioptrics) and curved mirrors (catoptrics). Catadioptric combinations are used in focusing systems such as searchlights, headlamps, early lighthouse focusing systems, optical telescopes, microscopes, and telephoto lenses. Other optical systems that use lenses and mirrors are also referred to as "catadioptric", such as surveillance catadioptric sensors.
The Maksutov is a catadioptric telescope design that combines a spherical mirror with a weakly negative meniscus lens in a design that takes advantage of all the surfaces being nearly "spherically symmetrical". The negative lens is usually full diameter and placed at the entrance pupil of the telescope. The design corrects the problems of off-axis aberrations such as coma found in reflecting telescopes while also correcting chromatic aberration. It was patented in 1941 by Russian optician Dmitri Dmitrievich Maksutov. Maksutov based his design on the idea behind the Schmidt camera of using the spherical errors of a negative lens to correct the opposite errors in a spherical primary mirror. The design is most commonly seen in a Cassegrain variation, with an integrated secondary, that can use all-spherical elements, thereby simplifying fabrication. Maksutov telescopes have been sold on the amateur market since the 1950s.
The Schmidt–Cassegrain is a catadioptric telescope that combines a Cassegrain reflector's optical path with a Schmidt corrector plate to make a compact astronomical instrument that uses simple spherical surfaces.
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas, the main characteristic being that the optical path folds back onto itself, relative to the optical system's primary mirror entrance aperture. This design puts the focal point at a convenient location behind the primary mirror and the convex secondary adds a telephoto effect creating a much longer focal length in a mechanically short system.
An aspheric lens or asphere is a lens whose surface profiles are not portions of a sphere or cylinder. In photography, a lens assembly that includes an aspheric element is often called an aspherical lens.
The Argunov–Cassegrain telescope is a catadioptric telescope design first introduced in 1972 by P. P. Argunov. All optics are spherical, and the classical Cassegrain secondary mirror is replaced by a sub-aperture secondary corrector group consisting of three air-spaced elements, two lenses and a Mangin mirror.
The Houghton telescope or Lurie–Houghton telescope is a catadioptric telescope. Houghton's original design uses a two-lens corrector at the front of the telescope and a spherical mirror at the back; it was patented in 1944. Instead of the hard to make intricately shaped compound curve Schmidt corrector plate, or the heavy Maksutov-type meniscus corrector lens, the Houghton double-lens corrector is relatively easy to make.
In optics, a Mangin mirror is a negative meniscus lens with the reflective surface on the rear side of the glass forming a curved mirror that reflects light without spherical aberration if certain conditions are met. This reflector was invented in 1876 by a French officer Alphonse Mangin as an improved catadioptric reflector for search lights and is also used in other optical devices.
An anastigmat or anastigmatic lens is a photographic lens completely corrected for the three main optical aberrations: spherical aberration, coma, and astigmatism. Early lenses often included the word Anastigmat in their name to advertise this new feature.
Sky-Watcher is a commercial distribution company established in 1999 by the Synta Technology Corporation of Taiwan that markets telescopes and astronomical equipment, like mounts and eyepieces, aimed at the amateur astronomical market. The products are manufactured at Synta Taiwan's Suzhou Synta Optical Technology Co., Ltd. in Suzhou (Jiangsu), China. The brand is distributed in Canada and Europe and, in the late 2000s, was extended to the USA market.
The Klevtsov–Cassegrain telescope is a type of catadioptric Cassegrain telescope that uses a spherical primary mirror and a sub-aperture secondary corrector group composed of a small lens and a Mangin mirror.
A meniscus corrector is a negative meniscus lens that is used to correct spherical aberration in image-forming optical systems such as catadioptric telescopes. It works by having the equal but opposite spherical aberration of the objective it is designed to correct.
A three-mirror anastigmat is an anastigmat telescope built with three curved mirrors, enabling it to minimize all three main optical aberrations – spherical aberration, coma, and astigmatism. This is primarily used to enable wide fields of view, much larger than possible with telescopes with just one or two curved surfaces.
