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Image of a refracting telescope from the Cincinnati Observatory in 1848
Image of a refracting telescope from the Cincinnati Observatory in 1848

A refracting or refractor telescope is a dioptric telescope that uses a lens as its objective to form an image. Dioptrics is the study of the Refraction of light especially by lenses. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging An objective in Optics is the lens or Mirror in a Microscope, Telescope, camera or other optical instrument The refracting telescope design was originally used in spy glasses and astronomical telescopes but is also used in other devices such as binoculars and long or telephoto camera lenses. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study Binocular telescopes, or binoculars (also known as field glasses are two identical or Mirror - symmetrical telescopes mounted side-by-side and

Contents

Invention

Main article: History of telescopes

Refractors were the earliest type of optical telescope. An optical telescope is a Telescope which is used to gather and focus light mainly from the visible part of the Electromagnetic spectrum The first practical refracting telescopes appeared in the Netherlands in about 1608, and were credited to three individuals, Hans Lippershey and Zacharias Janssen, spectacle-makers in Middelburg, and Jacob Metius of Alkmaar also known as Jacob Adriaanszoon. The Netherlands ( Dutch:, ˈnedərlɑnt is the European part of the Kingdom of the Netherlands, which consists of the Netherlands the Netherlands Hans Lippershey (1570&ndashSeptember 1619 also known as Johann Lippershey or Lipperhey, was a German - Dutch lensmaker. Sacharias Jansen (c 1585 - c 1632 was a Dutch spectacle-maker from Middelburg credited with inventing or contributing advances towards the invention of the This is about the city in the Netherlands For other uses see Middelburg (disambiguation. Jacob ( Jacobus; sometimes James) Metius (after 1571 Alkmaar - 1628 Alkmaar was a Dutch instrument-maker and optician For the place with the same name in Commewijne District of Suriname, see Alkmaar (Suriname. Galileo, happening to be in Venice in about the month of May 1609, heard of the invention and constructed a much improved version of his own based on his understanding of the effects of refraction. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher Venice ( Italian: Venezia, Venetian: Venesia or Venexia) is a city in Northern Italy, the capital of the Galileo then communicated the details of his invention to the public, and presented the instrument itself to the doge Leonardo Donato, sitting in full council. The Doge ( Venetian language, also Doxe, derived from Latin Dux military leader duke cf Galileo may thus claim to have invented the refracting telescope independently, but not until he had heard that others had done so.

Refracting telescope designs

Schematic of a Keplerian refracting telescope.
Schematic of a Keplerian refracting telescope.

All refracting telescopes use the same principles. The combination of an objective lenses (1) and some type of eyepiece (2) is used to gathered more light than the human eye could collect on its own, focus it (5), and present the viewer with a brighter, clearer, and magnified virtual image (6). An objective in Optics is the lens or Mirror in a Microscope, Telescope, camera or other optical instrument A lens is an optical device with perfect or approximate Axial symmetry which transmits and refracts Light, converging or diverging For the device for looking through a camera see Viewfinder. An eyepiece, or ocular lens, is a type of lens that is attached Brightness is an attribute of Visual perception in which a source appears to emit or reflect a given amount of Light. Magnification is the process of enlarging something only in appearance not in physical size In Optics, a virtual image is an image in which the outgoing rays from a point on the object never actually intersect at a point The objective in a refracting telescope refracts or bends light. Refraction is the change in direction of a Wave due to a change in its Speed. Light, or visible light, is Electromagnetic radiation of a Wavelength that is visible to the Human eye (about 400–700 This refraction causes parallel light rays to converge at a focal point; while those which were not parallel converge upon a focal plane. Track listing Child – 516 All I Need – 355 The cardinal points and the associated cardinal planes are a set of special points and planes in an optical system which help in the analysis Refracting telescopes can come in many different configurations to correct for image orientation and types of aberration. Because the image was formed by the bending of light, or refraction, these telescopes are called refracting telescopes or refractors.

Galilean telescope

The original design Galileo came up with in 1608 is commonly called a Galilean telescope. It uses a convex objective lens and a concave eyepiece lens.

Galileo’s best telescope magnified objects about 30 times. Because of flaws in its design, such as the shape of the lens, the images were blurry and distorted. Despite these flaws, the telescope was still good enough for Galileo to explore the sky.

Keplerian Telescope

The Keplerian Telescope, invented by Johannes Kepler in 1611, is an improvement on Galileo's design. Johannes Kepler (ˈkɛplɚ ( December 27 1571 &ndash November 15 1630) was a German Mathematician, Astronomer It uses a convex lens as the eyepiece instead of Galileo's concave one. The advantage of this arrangement is the rays of light emerging from the eyepiece are converging. This allows for a much wider field of view and greater eye relief but the image for the viewer is inverted. Considerably higher magnifications can be reached with this design but to overcome aberrations the simple objective lens needs to have a very high f-ratio (Johannes Hevelius built one with a 45 m (150 ft) focal length). Johannes Hevelius ( Latin) also called Johannes Hewel Johann Hewelke Johannes Höwelcke in German, or Jan Heweliusz (in Polish) The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. The design also allows for use of a micrometer at the focal plane (used to determining the angular size and/or distance between objects observed). A filar micrometer is a device used in astronomical telescopes for precision measurements

Achromatic refractors

Main article: Achromatic telescope

The Achromatic refracting lens was invented in 1733 by an English barrister named Chester Moore Hall although it was independently invented and patented by John Dollond around 1758. The achromatic telescope is a Refracting telescope that uses an Achromatic lens to correct for Chromatic aberration. An achromatic lens or achromat is a lens that is designed to limit the effects of chromatic and Spherical aberration. Chester Moore Hall (1703–1771 was a British lawyer who produced the first Achromatic lenses in 1729 or 1733 (accounts differ John Dollond ( June 10, 1706 - November 30, 1761) was an English Optician. The design overcame the need for very long focal legths in refracting telescopes by using an objective made of two pieces of glass with different dispersion, "crown" and "flint glass", to limit the effects of chromatic and spherical aberration. Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many In Optics, dispersion is the phenomenon in which the Phase velocity of a wave depends on its frequency Crown glass is type of optical glass used in lenses and other optical components Flint Glass is an experimental electronic project by French electronic musician Gwenn Trémorin In Optics, chromatic aberration is caused by a lens having a different Refractive index for different Wavelengths of Light spherical-aberration-diskjpg|thumb|300 px|left|A Point source as imaged by a system with negative (top zero (center and positive (bottom spherical aberration Each side of each piece is ground and polished, and then the two pieces are assembled together. Polishing is the process of creating a smooth and shiny surface by using rubbing or a chemical action leaving a surface with significant Specular reflection and minimal Achromatic lenses are corrected to bring two wavelengths (typically red and blue) into focus in the same plane. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency.

Apochromatic refractors

Main article: Apochromat

Apochromatic refractors have objectives built with special, extra-low dispersion materials. They are designed to bring three wavelengths (typically red, green, and blue) into focus in the same plane. The residual color error (secondary spectrum) can be up to an order of magnitude less than that of an achromatic lens. Such telescopes contain elements of fluorite or special, extra-low dispersion (ED) glass in the objective and produce a very crisp image that is virtually free of chromatic aberration. Fluorite (also called fluorspar) is a Mineral composed of Calcium fluoride, Ca[[Fluorine F2]] Such telescopes are sold in the high-end amateur telescope market. Apochromatic refractors are available with objectives of up to 553 mm in diameter, but most are between 80 and 152 mm.

Technical considerations

Refractors have been criticized for their relatively high-degree of residual chromatic and spherical aberration. In Optics, chromatic aberration is caused by a lens having a different Refractive index for different Wavelengths of Light spherical-aberration-diskjpg|thumb|300 px|left|A Point source as imaged by a system with negative (top zero (center and positive (bottom spherical aberration This affects shorter focal lengths more than longer ones. The focal length of an optical system is a measure of how strongly it converges (focuses or diverges (diffuses Light. A 4" f/6 achromatic refractor is likely to show considerable color fringing (generally a purple halo around bright objects). A 4" f/16 will have little color fringing.

In very large apertures, there is also a problem of lens sagging, a result of gravity deforming glass. Lens sag is a problem that sometimes afflicts very large Refracting telescopes It is the equivalent of mirror sag in Reflecting telescopes It occurs when the physical Gravitation is a natural Phenomenon by which objects with Mass attract one another Glass in the common sense refers to a Hard, Brittle, transparent Solid, such as that used for Windows many There is a further problem of glass defects, striae or small air bubbles trapped within the glass. Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five In addition, glass is opaque to certain wavelengths, and even visible light is dimmed by reflection and absorption when it crosses the air-glass interfaces and passes through the glass itself. Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation especially visible Light. In Physics wavelength is the distance between repeating units of a propagating Wave of a given Frequency. Most of these problems are avoided or diminished by using reflecting telescopes, that can be made in far larger apertures. A reflecting telescope (also called a reflector) is an Optical telescope which uses a single or combination of Curved mirrors that reflect Light

Notable refracting telescopes

The 76 cm refractor at Nice Observatory. A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth The Observatoire de Nice ( Nice Observatory) is located in Nice, France on the summit of Mont Gros.

20 inch refractor at the Observatories at Chabot Space & Science Center in Oakland, California. Inches redirects here To see the Les Savy Fav album see Inches. Chabot Space and Science Center, located in Oakland California, is a hands-on center featuring interactive exhibits a digital Planetarium, a large screen theater Oakland (ˈoʊklənd founded in 1852 is the eighth-largest city in the U

8 inch refractor at the Observatories at Chabot Space & Science Center in Oakland, California. Inches redirects here To see the Les Savy Fav album see Inches. Chabot Space and Science Center, located in Oakland California, is a hands-on center featuring interactive exhibits a digital Planetarium, a large screen theater Oakland (ˈoʊklənd founded in 1852 is the eighth-largest city in the U

The 68 cm refractor at the Vienna University Observatory. A centimetre ( American spelling: centimeter, symbol cm) is a unit of Length in the Metric system, equal to one hundredth Universitäts-Sternwarte Wien ( Vienna Observatory) is an astronomical Observatory in Vienna, Austria.

The Great Refractor at the Archenhold Observatory in Berlin. The Archenhold Observatory, named in honor of Friedrich Simon Archenhold, is an Observatory in Berlin-Treptow.

Refractor at the Observatory in Aachen, Germany

See also

( Ripuarian: Oche, Dutch: Aken, Spanish: Aquisgrán, Italian: Aquisgrana, French, Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. A reflecting telescope (also called a reflector) is an Optical telescope which uses a single or combination of Curved mirrors that reflect Light A catadioptric optical system is one which contains both lenses and Mirrors Catadioptric systems are commonly used in Telescopes and in lightweight An Astrograph ( astrographic camera) is a telescope designed for the sole purpose of Astrophotography. Here is a list of the largest optical Refracting telescopes sorted by lens diameter and focal length

Dictionary

refracting telescope

-noun

  1. A telescope which produces a magnified image by refracting light through a series of lenses housed in a tube, with a light-gathering objective lens at one end and an eyepiece at the other. Also called a refractor.
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