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47-792: The MPG/ESO telescope is a 2.2-metre f/8.0 (17.6-metre) ground-based telescope at the European Southern Observatory (ESO) in La Silla , Chile . It was built by Zeiss and has been operating since 1984. It was on indefinite loan to the European Southern Observatory from the Max Planck Institute for Astronomy (MPIA). In October 2013 it was returned to the MPIA. Telescope time is shared between MPIA and MPE observing programmes, while

94-445: A compound lens. The most common type is an achromatic doublet , with elements made of crown and flint glass . This reduces the amount of chromatic aberration over a certain range of wavelengths, though it does not produce perfect correction. By combining more than two lenses of different composition, the degree of correction can be further increased, as seen in an apochromatic lens or apochromat . "Achromat" and "apochromat" refer to

141-478: A digital camera, very small highlights may frequently appear to have chromatic aberration where in fact the effect is because the highlight image is too small to stimulate all three color pixels, and so is recorded with an incorrect color. This may not occur with all types of digital camera sensor. Again, the de-mosaicing algorithm may affect the apparent degree of the problem. Chromatic aberration also affects black-and-white photography. Although there are no colors in

188-544: A few bands can be observed from the Earth's surface. These bands are visible – near-infrared and a portion of the radio-wave part of the spectrum. For this reason there are no X-ray or far-infrared ground-based telescopes as these have to be observed from orbit. Even if a wavelength is observable from the ground, it might still be advantageous to place a telescope on a satellite due to issues such as clouds, astronomical seeing and light pollution . The disadvantages of launching

235-504: A focal point. Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits ), spotting scopes , monoculars , binoculars , camera lenses , and spyglasses . There are three main optical types: A Fresnel imager is a proposed ultra-lightweight design for a space telescope that uses a Fresnel lens to focus light. Beyond these basic optical types there are many sub-types of varying optical design classified by

282-584: A lens that is optically well-corrected for chromatic aberration would for the following reasons: The above are closely related to the specific scene that is captured so no amount of programming and knowledge of the capturing equipment (e.g., camera and lens data) can overcome these limitations. The term " purple fringing " is commonly used in photography , although not all purple fringing can be attributed to chromatic aberration. Similar colored fringing around highlights may also be caused by lens flare . Colored fringing around highlights or dark regions may be due to

329-546: A lower weight and size than traditional optics of similar specifications and are generally well-regarded by wildlife photographers. For a doublet consisting of two thin lenses in contact, the Abbe number of the lens materials is used to calculate the correct focal length of the lenses to ensure correction of chromatic aberration. If the focal lengths of the two lenses for light at the yellow Fraunhofer D-line (589.2 nm) are f 1 and f 2 , then best correction occurs for

376-419: A mirror instead of a lens was being investigated soon after the invention of the refracting telescope. The potential advantages of using parabolic mirrors —reduction of spherical aberration and no chromatic aberration —led to many proposed designs and several attempts to build reflecting telescopes . In 1668, Isaac Newton built the first practical reflecting telescope, of a design which now bears his name,

423-550: A negative Abbe number of −3.5. Diffractive optical elements can be fabricated using diamond turning techniques. Telephoto lenses using diffractive elements to minimize chromatic aberration are commercially available from Canon and Nikon for interchangeable-lens cameras; these include 800mm f/6.3, 500mm f/5.6, and 300mm f/4 models by Nikon (branded as "phase fresnel" or PF), and 800mm f/11, 600mm f/11, and 400mm f/4 models by Canon (branded as "diffractive optics" or DO). They produce sharp images with reduced chromatic aberration at

470-475: A single receiver and records a single time-varying signal characteristic of the observed region; this signal may be sampled at various frequencies. In some newer radio telescope designs, a single dish contains an array of several receivers; this is known as a focal-plane array . By collecting and correlating signals simultaneously received by several dishes, high-resolution images can be computed. Such multi-dish arrays are known as astronomical interferometers and

517-625: A space telescope include cost, size, maintainability and upgradability. Some examples of space telescopes from NASA are the Hubble Space Telescope that detects visible light, ultraviolet, and near-infrared wavelengths, the Spitzer Space Telescope that detects infrared radiation, and the Kepler Space Telescope that discovered thousands of exoplanets. The latest telescope that was launched was

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564-477: A telescope was a 1608 patent submitted to the government in the Netherlands by Middelburg spectacle maker Hans Lipperhey for a refracting telescope . The actual inventor is unknown but word of it spread through Europe. Galileo heard about it and, in 1609, built his own version, and made his telescopic observations of celestial objects. The idea that the objective , or light-gathering element, could be

611-482: Is also quite small. Many types of glass have been developed to reduce chromatic aberration. These are low dispersion glass , most notably, glasses containing fluorite . These hybridized glasses have a very low level of optical dispersion; only two compiled lenses made of these substances can yield a high level of correction. The use of achromats was an important step in the development of optical microscopes and telescopes . An alternative to achromatic doublets

658-412: Is called an observatory . Radio telescopes are directional radio antennas that typically employ a large dish to collect radio waves. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed. Unlike an optical telescope, which produces a magnified image of the patch of sky being observed, a traditional radio telescope dish contains

705-528: Is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and aperture masking interferometry at single reflecting telescopes. Radio telescopes are also used to collect microwave radiation , which has the advantage of being able to pass through the atmosphere and interstellar gas and dust clouds. Some radio telescopes such as the Allen Telescope Array are used by programs such as SETI and

752-482: Is possible to make very tiny antenna). The near-infrared can be collected much like visible light; however, in the far-infrared and submillimetre range, telescopes can operate more like a radio telescope. For example, the James Clerk Maxwell Telescope observes from wavelengths from 3 μm (0.003 mm) to 2000 μm (2 mm), but uses a parabolic aluminum antenna. On the other hand,

799-572: Is sharper. If the prescription is right, then the cornea, lens and prescribed lens will focus the red and green wavelengths just in front, and behind the retina, appearing of equal sharpness. If the lens is too powerful or weak, then one will focus on the retina, and the other will be much more blurred in comparison. In some circumstances, it is possible to correct some of the effects of chromatic aberration in digital post-processing. However, in real-world circumstances, chromatic aberration results in permanent loss of some image detail. Detailed knowledge of

846-400: Is the use of diffractive optical elements. Diffractive optical elements are able to generate arbitrary complex wave fronts from a sample of optical material which is essentially flat. Diffractive optical elements have negative dispersion characteristics, complementary to the positive Abbe numbers of optical glasses and plastics. Specifically, in the visible part of the spectrum diffractives have

893-406: Is underway on several 30–40m designs. The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays . The first purpose-built radio telescope went into operation in 1937. Since then, a large variety of complex astronomical instruments have been developed. Since the atmosphere is opaque for most of the electromagnetic spectrum, only

940-645: The Arecibo Observatory to search for extraterrestrial life. An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum. Optical telescopes increase the apparent angular size of distant objects as well as their apparent brightness . For the image to be observed, photographed, studied, and sent to a computer, telescopes work by employing one or more curved optical elements, usually made from glass lenses and/or mirrors , to gather light and other electromagnetic radiation to bring that light or radiation to

987-822: The Earth's atmosphere is opaque to this part of the electromagnetic spectrum. An example of this type of telescope is the Fermi Gamma-ray Space Telescope which was launched in June 2008. The detection of very high energy gamma rays, with shorter wavelength and higher frequency than regular gamma rays, requires further specialization. Such detections can be made either with the Imaging Atmospheric Cherenkov Telescopes (IACTs) or with Water Cherenkov Detectors (WCDs). Examples of IACTs are H.E.S.S. and VERITAS with

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1034-405: The Netherlands at the beginning of the 17th century. They were used for both terrestrial applications and astronomy . The reflecting telescope , which uses mirrors to collect and focus light, was invented within a few decades of the first refracting telescope. In the 20th century, many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in

1081-504: The Newtonian reflector . The invention of the achromatic lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter, more functional refracting telescopes. Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century—a problem alleviated by

1128-572: The Spitzer Space Telescope , observing from about 3 μm (0.003 mm) to 180 μm (0.18 mm) uses a mirror (reflecting optics). Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe in the frequency range from about 0.2 μm (0.0002 mm) to 1.7 μm (0.0017 mm) (from ultra-violet to infrared light). With photons of the shorter wavelengths, with

1175-415: The type of correction (2 or 3 wavelengths correctly focused), not the degree (how defocused the other wavelengths are), and an achromat made with sufficiently low dispersion glass can yield significantly better correction than an achromat made with more conventional glass. Similarly, the benefit of apochromats is not simply that they focus three wavelengths sharply, but that their error on other wavelengths

1222-764: The 1960s. The word telescope was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei 's instruments presented at a banquet at the Accademia dei Lincei . In the Starry Messenger , Galileo had used the Latin term perspicillum . The root of the word is from the Ancient Greek τῆλε, romanized tele 'far' and σκοπεῖν, skopein 'to look or see'; τηλεσκόπος, teleskopos 'far-seeing'. The earliest existing record of

1269-627: The James Webb Space Telescope on December 25, 2021, in Kourou, French Guiana. The Webb telescope detects infrared light. The name "telescope" covers a wide range of instruments. Most detect electromagnetic radiation , but there are major differences in how astronomers must go about collecting light (electromagnetic radiation) in different frequency bands. As wavelengths become longer, it becomes easier to use antenna technology to interact with electromagnetic radiation (although it

1316-462: The condition: where V 1 and V 2 are the Abbe numbers of the materials of the first and second lenses, respectively. Since Abbe numbers are positive, one of the focal lengths must be negative, i.e., a diverging lens, for the condition to be met. The overall focal length of the doublet f is given by the standard formula for thin lenses in contact: and the above condition ensures this will be

1363-470: The first reflecting telescope , his Newtonian telescope , in 1668. ) Modern telescopes, as well as other catoptric and catadioptric systems , continue to use mirrors, which have no chromatic aberration. There exists a point called the circle of least confusion , where chromatic aberration can be minimized. It can be further minimized by using an achromatic lens or achromat , in which materials with differing dispersion are assembled together to form

1410-421: The focal length of the doublet for light at the blue and red Fraunhofer F and C lines (486.1 nm and 656.3 nm respectively). The focal length for light at other visible wavelengths will be similar but not exactly equal to this. Chromatic aberration is used during a duochrome eye test to ensure that a correct lens power has been selected. The patient is confronted with red and green images and asked which

1457-682: The higher frequencies, glancing-incident optics, rather than fully reflecting optics are used. Telescopes such as TRACE and SOHO use special mirrors to reflect extreme ultraviolet , producing higher resolution and brighter images than are otherwise possible. A larger aperture does not just mean that more light is collected, it also enables a finer angular resolution. Telescopes may also be classified by location: ground telescope, space telescope , or flying telescope . They may also be classified by whether they are operated by professional astronomers or amateur astronomers . A vehicle or permanent campus containing one or more telescopes or other instruments

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1504-417: The image and is specified by optical engineers, optometrists, and vision scientists in diopters . It can be reduced by stopping down , which increases depth of field so that though the different wavelengths focus at different distances, they are still in acceptable focus. Transverse CA does not occur on the optical axis of an optical system (which is typically the center of the image) and increases away from

1551-528: The incorrect focusing of red and blue results in purple fringing around highlights. This is a uniform problem across the frame, and is more of a problem in CCDs with a very small pixel pitch such as those used in compact cameras. Some cameras, such as the Panasonic Lumix series and newer Nikon and Sony DSLRs , feature a processing step specifically designed to remove it. On photographs taken using

1598-415: The introduction of silver coated glass mirrors in 1857, and aluminized mirrors in 1932. The maximum physical size limit for refracting telescopes is about 1 meter (39 inches), dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been reflectors. The largest reflecting telescopes currently have objectives larger than 10 meters (33 feet), and work

1645-571: The lens (focus shift ). Longitudinal aberration is typical at long focal lengths. Transverse aberration occurs when different wavelengths are focused at different positions in the focal plane , because the magnification and/or distortion of the lens also varies with wavelength. Transverse aberration is typical at short focal lengths. The ambiguous acronym LCA is sometimes used for either longitudinal or lateral chromatic aberration. The two types of chromatic aberration have different characteristics, and may occur together. Axial CA occurs throughout

1692-752: The next-generation gamma-ray telescope, the Cherenkov Telescope Array ( CTA ), currently under construction. HAWC and LHAASO are examples of gamma-ray detectors based on the Water Cherenkov Detectors. A discovery in 2012 may allow focusing gamma-ray telescopes. At photon energies greater than 700 keV, the index of refraction starts to increase again. Chromatic aberration There are two types of chromatic aberration: axial ( longitudinal ), and transverse ( lateral ). Axial aberration occurs when different wavelengths of light are focused at different distances from

1739-586: The operation and maintenance of the telescope are ESO's responsibility. The telescope hosts three instruments: the 67-million-pixel Wide Field Imager with a field of view able to cover the full Moon; GROND, the Gamma-Ray Burst Optical/Near-Infrared Detector , which chases the afterglows of the most powerful explosions in the universe, known as gamma-ray bursts; and the high-resolution spectrograph , FEROS, used to make detailed studies of stars. In November 2010 it

1786-534: The optical axis. It is not affected by stopping down since it is caused by the different magnification of the lens with each color of light. In digital sensors, axial CA results in the red and blue planes being defocused (assuming that the green plane is in focus), which is relatively difficult to remedy in post-processing, while transverse CA results in the red, green, and blue planes being at different magnifications (magnification changing along radii, as in geometric distortion ), and can be corrected by radially scaling

1833-1037: The optical system used to produce the image can allow for some useful correction. In an ideal situation, post-processing to remove or correct lateral chromatic aberration would involve scaling the fringed color channels, or subtracting some of a scaled versions of the fringed channels, so that all channels spatially overlap each other correctly in the final image. As chromatic aberration is complex (due to its relationship to focal length, etc.) some camera manufacturers employ lens-specific chromatic aberration appearance minimization techniques. Almost every major camera manufacturer enables some form of chromatic aberration correction, both in-camera and via their proprietary software. Third-party software tools such as PTLens are also capable of performing complex chromatic aberration appearance minimization with their large database of cameras and lens. In reality, even theoretically perfect post-processing based chromatic aberration reduction-removal-correction systems do not increase image detail as well as

1880-488: The planes appropriately so they line up. In the earliest uses of lenses, chromatic aberration was reduced by increasing the focal length of the lens where possible. For example, this could result in extremely long telescopes such as the very long aerial telescopes of the 17th century. Isaac Newton 's theories about white light being composed of a spectrum of colors led him to the conclusion that uneven refraction of light caused chromatic aberration (leading him to build

1927-624: The rays just a few degrees . The mirrors are usually a section of a rotated parabola and a hyperbola , or ellipse . In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror. Examples of space observatories using this type of telescope are the Einstein Observatory , ROSAT , and the Chandra X-ray Observatory . In 2012 the NuSTAR X-ray Telescope

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1974-533: The receptors for different colors having differing dynamic range or sensitivity – therefore preserving detail in one or two color channels, while "blowing out" or failing to register, in the other channel or channels. On digital cameras, the particular demosaicing algorithm is likely to affect the apparent degree of this problem. Another cause of this fringing is chromatic aberration in the very small microlenses used to collect more light for each CCD pixel; since these lenses are tuned to correctly focus green light,

2021-511: The task they perform such as astrographs , comet seekers and solar telescopes . Most ultraviolet light is absorbed by the Earth's atmosphere, so observations at these wavelengths must be performed from the upper atmosphere or from space. X-rays are much harder to collect and focus than electromagnetic radiation of longer wavelengths. X-ray telescopes can use X-ray optics , such as Wolter telescopes composed of ring-shaped 'glancing' mirrors made of heavy metals that are able to reflect

2068-519: The technique is called aperture synthesis . The 'virtual' apertures of these arrays are similar in size to the distance between the telescopes. As of 2005, the record array size is many times the diameter of the Earth – using space-based very-long-baseline interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite. Aperture synthesis

2115-439: Was an optical instrument using lenses , curved mirrors , or a combination of both to observe distant objects – an optical telescope . Nowadays, the word "telescope" is defined as a wide range of instruments capable of detecting different regions of the electromagnetic spectrum , and in some cases other types of detectors. The first known practical telescopes were refracting telescopes with glass lenses and were invented in

2162-447: Was launched which uses Wolter telescope design optics at the end of a long deployable mast to enable photon energies of 79 keV. Higher energy X-ray and gamma ray telescopes refrain from focusing completely and use coded aperture masks: the patterns of the shadow the mask creates can be reconstructed to form an image. X-ray and Gamma-ray telescopes are usually installed on high-flying balloons or Earth-orbiting satellites since

2209-427: Was used to observe HIP 13044 , and marked what was thought to be the first time a planetary system in a stellar stream of extragalactic origin had been detected. However, subsequent analysis in 2014 found no evidence for a planet orbiting the star. Telescope A telescope is a device used to observe distant objects by their emission, absorption , or reflection of electromagnetic radiation . Originally, it

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