List of largest optical telescopes in the 20th century


The following is a list of the largest optical telescopes in the 20th century, paying special attention to the diameter of the mirror or lens of the telescope's objective, or aperture. Aperture rank currently goes approximately by the usable physical aperture size and not by aperture synthesis, although interferometers attained some of the highest angular resolutions at visible and infrared wavelengths compared to traditional telescopes. Diverging methods of construction and use for reflecting telescopes in that area make comparing synthesized aperture irregular.
For instance, Keck I or II alone has less angular resolution than the Keck Interferometer, however, the Keck Interferometer is used for a much narrower range of type of observations. Ultimately, a valid comparison between two telescopes must take into consideration more specifications, when a general measurement becomes obtuse.
Aperture of the primary mirror alone can be poor measure of a reflective telescope's significance; for example, the Hubble Space Telescope has only a primary mirror. In addition, many large or significant telescopes are not optical and/or reflecting. However, many famous optical telescopes have had large apertures on their primary mirror with corresponding good angular resolution.
Including optical observatories, including UV, visible and some optical infrared telescopes, near infrared. Covers from about 1901 to 2001, with some flexibility to accommodate ambiguity in classification, for example some 2002 telescope, if it was nearly operation in 2001. 19th century and earlier telescopes that ceased operation are not included, but the list is not complete.

Table of optical telescopes

Multiple mirror telescopes are ranked by their equivalent optical area, not peak interferometric aperture unless it is not relevant for the design. See also List of astronomical interferometers at visible and infrared wavelengths.
See also List of largest optical refracting telescopes, as this list does yet not include such large refractors as the Yerkes Observatory.
Name/ObservatoryAperture
m
Aper.
in
Mirror typeNationality of SponsorsSite and/or ObservatoryFL or BuiltImage
Keck 110 m394″Segmented,36United StatesMauna Kea Observatory, Hawaii1993
Keck 210 m394″Segmented,36United StatesMauna Kea Observatory, Hawaii1996
Hobby-Eberly Telescope 9.2 m362″Segmented,91United States, GermanyMcDonald Observatory, Texas1997
Subaru 8.2 m323″SingleJapanMauna Kea Observatory, Hawaii1999
VLT 1 8.2 m323″SingleESO Countries + ChileParanal Observatory, Chile1998
VLT 2 8.2 m323″SingleESO Countries + ChileParanal Observatory, Chile1999-
VLT 3 8.2 m323″SingleESO Countries + ChileParanal Observatory, Chile2000*-
VLT 4 8.2 m323″SingleESO Countries + ChileParanal Observatory, Chile2001*-
Gemini North 8.1 m318″SingleUnited States, Canada, Chile, Australia, Argentina, BrazilMauna Kea Obs., Hawaii1999
Gemini South8.1 m318″SingleUnited States, Canada, Chile, Australia, Argentina, BrazilCerro Pachón, Chile2001-
MMT6.5 m256″SingleUnited StatesF. L. Whipple Obs., Arizona2000-
Magellan 1 6.5 m256″HoneycombUnited StatesLas Campanas Obs., Chile2000
Magellan 2 6.5 m256″HoneycombUnited StatesLas Campanas Obs., Chile2002*-
BTA-66 m238″SingleUSSR + RussiaZelenchukskaya, Caucasus1976-
Hale Telescope 5.08 m200″SingleUnited StatesPalomar Observatory, California1948
MMT optics replaced4.7 m 186″6 mirrorsUnited StatesF. L. Whipple Obs., Arizona1979–1998-
William Herschel Telescope4.2 m165″SingleUK, Netherlands, SpainORM, Canary Islands1987
SOAR4.1 m161″SingleUnited States, BrazilCerro Pachón, Chile2002*
Nicholas U. Mayall 4m4 m158″SingleUSAKitt Peak National Obs.; Arizona1973
Victor M. Blanco Telescope4 m158″SingleUSACerro Tololo Inter-American Obs., Chile1976
Anglo-Australian Telescope 3.89 m154″SingleUnited Kingdom + AustraliaAnglo-Australian Obs.; Siding Spring, Australia1975
United Kingdom Infrared Telescope 3.8 m150″Single IRUnited KingdomMauna Kea Observatories; Mauna Kea, Hawaii1978-
3.67m AEOS Telescope 3.67 m145″SingleUnited StatesAir Force Maui Optical Station; Haleakala, Hawaii1996-
Telescopio Nazionale Galileo 3.58 m138″SingleItalyORM; La Palma, Canary Islands1997
New Technology Telescope 3.58 m142″SingleESO countriesEuropean Southern Observatory; Cerro La Silla, Chile1989
Canada-France-Hawaii Telescope 3.58 m141″SingleCanada, France, United StatesMauna Kea Observatories, USA1979
ESO 3.6 m Telescope3.57 m140″SingleESO countriesEuropean Southern Observatory; Cerro La Silla, Chile1977
MPI-CAHA 3.5m3.5 m138″SingleWest Germany+SpainCalar Alto Obs., Spain1984-
USAF Starfire 3.5m3.5 m138″SingleUSAStarfire Optical Range; New Mexico1994
WIYN Telescope3.5 m138″SingleUSAKitt Peak National Obs., USA1994
Astrophysical Research Consortium 3.48 m137″SingleUSAApache Point Obs.; Sacramento Peak, New Mexico1994-
Shane Telescope3.05 m120″SingleUnited StatesLick Observatory; Mt. Hamilton, California1959
Infrared Telescope Facility 3 m118″Single IRUnited StatesMauna Kea, Hawaii1979-
NASA-LMT retired3 m118″LiquidUSASacramento Peak, New Mexico, USA1995–2002-
Harlan J. Smith Telescope2.72 m107″SingleUSAMcDonald Observatory, Texas, USA1969-
UBC-Laval LMT2.65 m104″LiquidCanadaVancouver, Canada1992–-
Shajn 2.6m 2.64 m103″SingleCrimean Astrophysical Obs., Ukraine1961-
BAO 2.62.6 m102″SingleByurakan Astrophysical Obs.; Mt. Aragatz, Armenia1976-
Nordic Optical Telescope 2.56 m101″SingleDenmark, Sweden, Iceland, Norway, FinlandLa Palma, Canary Islands1988
Isaac Newton Telescope 2.54 m100″ZerodurUKLa Palma, Canary Islands moved/new mirror1984
du Pont2.54 m100″SingleUSALas Campanas Observatory, Chile1976-
Hooker 100-Inch Telescope2.54 m100″SingleUnited StatesMt. Wilson Observatory; California1917-
Sloan DSS2.5 m98″SingleUnited StatesSacramento Peak, New Mexico1997-
Isaac Newton Telescope 2.54 m98″SingleUKRGO, Sussex, England 1965–1979-
Hiltner Telescope2.4 m95″SingleUnited StatesMDM Observatory, Kitt Peak, Arizona1986-
Hubble 2.4 m94″SingleNASA+ESALow Earth orbit1990-
Vainu Bappu2.34 m92″SingleVainu Bappu Observatory, India1986-
WIRO 2.32.3 m90.5″SingleUSAWyoming, USA1977-
ANU 2.3m ATT2.3 m90″SingleAustraliaSiding Spring Obs., Australia1984-
Bok Telescope 2.3 m90″SingleUSASteward Obs., Kitt Peak, Arizona1969-
University of Hawaii 2.2 m2.24 m88″SingleUSAMauna Kea Observatories, Hawaii1970-
MPIA-ESO 2.2 m87″SingleWest GermanyCerro La Silla, Chile1984-
MPIA-CAHA 2.2m2.2 m87″SingleWest GermanyCalar Alto Observatory, Spain1979-
Xinglong 2.16m2.16 m85″SinglePRC Xinglong, China1989-
Jorge Sahade 2.15m2.15 m84″SingleLeoncito Astronomical Complex, Argentina1987-
INAOE 2.12 2.12 m83″SingleMexico, USAGuillermo Haro Observatory; Sonora1987-
UNAM 2.122.12 m83"SingleNAO; San Pedro, Mexico1979-
Kitt Peak 2.1-meter2.1 m83″SingleUSAKitt Peak, USA1964-
Otto Struve Telescope2.1 m82SingleUSAMcDonald Observatory, USA1939-
Himalayan Chandra Telescope 2.01 m79″SingleIndiaIndian Astronomical Obs., Hanle 2000-
Alfred Jensch Teleskop2 m79″SingleKarl Schwarzschild Observatory1960-
Carl Zeiss Jena2 m79″SingleShamakhi Astrophysical Obs., Azerbaijan1966-
Ondřejov 2-m 2 m79″SingleUSSR + CzechoslovakiaOndřejov Observatory, Czech1967
Ritchey-Chretien-Coude 2 m79″SingleRozhen Observatory, Bulgaria1984-
Carl Zeiss Jena2 m79″SingleMain Ukraine Obs.-
Bernard Lyot Telescope2 m79″SingleFrancePic du Midi Obs., France1980
Faulkes Telescope South2 m79″SingleUKSiding Spring Obs., Australia2001
MAGNUM2 m79″Single IRJapanHaleakala Obs., USA2001-
OHP 1.931.93 m76″SingleFranceHaute-Provence Observatory, France1958-
74 inch Radcliffe Telescope 1.88 m74″SingleSouth African Astronomical Obs., Sutherland, 1974–Present
Radcliffe Obs.,1948– 1974
1950-
188 cm telescope1.88 m74″SingleJapanOkayama Astrophysical Observatory, Japan1960-
DDO 1.88 m1.88 m74″SingleCanadaDavid Dunlap Observatory, Ontario1935-
74" reflector1.88 m74″SingleAustraliaMount Stromlo Observatory, Australia1955–2003-
Kottamia telescope 1.88 m1.88 m74″SingleEgyptEgypt1960-
Vatican Advanced Technology Telescope 1.83 m72″SingleVatican CityMt. Graham International Obs., Arizona1993-
72-Inch Perkins Telescope1.83 m72″SingleUSALowell Observatory, Anderson Mesa USA1964-
Plaskett telescope1.83 m72″SingleGreat BritainDominion Astrophysical Observatory, Canada1918-
Copernico 182 cm1.82 m72″SingleItalyAsiago Observatory, Italy 1973-
1.8m Ritchey Cretien reflector1.8 m72″SingleKoreaBohyunsan Optical Astronomy Observatory, Korea1996-
Sandy Cross Telescope1.8 m71″SingleCanadaRothney Astrophysical Observatory1996-
Spacewatch 1.8-meter Telescope1.8 m71″SingleUSAKitt Peak National Observatory, USA2001-
69-inch Perkins Telescope1.75 m69″SingleUSAPerkins Observatory, Ohio1931–1964-
165 cm telescope1.65 m65″SingleMoletai Astronomical Obs., Lithuania1991-
McMath-Pierce Solar Telescope1.61 m63″SingleUSAKitt Peak National Obs., USA1962
AZT-331.6 m63″SingleSayan Solar Obs., Siberia 1981-
1.6 m Perkin Elmer1.6 m63″SingleBrazilPico dos Dias Observatory1981-
1.61.6 m63″R/CCanadaMont Mégantic Observatory, Canada1978-
Kaj Strand Telescope1.55 m61″SingleUSAUSN Obs. Flagstaff Station,USA1964-
61" Kuiper Telescope1.55 m61″SingleUSASteward Obs., Mt. Bigelow, USA1965-
Oak Ridge Observatory 61" reflector 1.55 m61″SingleUSAOak Ridge Observatory, Massachusetts, USA1933-2005
-
Estación Astrofísica de Bosque Alegre1.54 m60.6″SingleArgentinaEstación Astrofísica de Bosque Alegre, Argentina1942-
Danish 1.54 meter telescope1.54 m60.6″SingleDenmarkLa Silla Observatory, Chile1979-
Harvard 60-inch Reflector1.524 m60″SingleUnited StatesHarvard College Observatory, USA1905–1931-
60-Inch Telescope1.524 m60″SingleUnited StatesMt. Wilson Observatory; California1908
Dunn Solar Telescope ex-VTT1.524 m60″SingleUSANational Solar Obs.-Sacramento Peak, USA1969-
Palomar Observatory 60 inch1.524 m60″SingleUSAPalomar Observatory, California, USA1970-
FLWO 1.5m Tillinghast1.52 m60″SingleUnited StatesF. L. Whipple Obs., Arizona1994-
Telescopio Carlos Sánchez 1.52 m60″SingleUK + SpainTeide Observatory, Tenerife 1971-
OHP 1.521.52 m60″SingleFranceHaute-Provence Obs., France1967-
Mt. Lemmon 60" Telescope1.52 m60″SingleUSASteward Observatory, Mount Lemmon, USA1970-
OAN 1.52 m1.52 m60″SingleSpainCalar Alto Observatory, Spain1970s-
152 cm G.D. Cassini1.52 m60″SingleItalyMount Orzale, Italy1976-
TIRGO 1.50 m59″Single IRItaly + SwitzerlandHochalpine Forschungsstation Jungfraujoch und Gornergrat, Alps, Switzerland 1979–2005-
AZT-221.5 m59″SingleUSSR, UzbekistanMount Maidanak, Uzbekistan1972-
AZT-201.5 m59″SingleAssy-Turgen Observatory, Kazakhstan-
AZT-121.5 m59″SingleUSSR, EstoniaTartu Observatory, Estonia1976-
RTT-1501.5 m59″SingleRussia, TurkeyTÜBİTAK National Observatory, Turkey2001-
OSN 1.5m 1.5 m59″SingleSpainSierra Nevada Obs., Spain 1991-
BST-1M1.5 m59″Single IRUSSRSalyut 6, Earth Orbit1977–1982-
USNOFS 1.3m1.3 m51″SingleUSAUSN Obs. Flagstaff Station,USA1998-
Warsaw Telescope1.3 m51″SinglePolandLas Campanas Obs., Chile1996-
Skinakas 1.3m Telescope1.3m51SingleGreeceSkinakas Obs., Greece1995-
McGraw-Hill Telescope1.27 m50″SingleUSAMDM Observatory, Arizona
Stinchfield Woods, Michigan
1969-
Great Melbourne Telescope 127 cm50″SingleAustraliaMount Stromlo Observatory, Australia1961-1973
1992-2003
-
AZT-111.25 m49″SingleAbastumani Obs., Georgia 1976-
AZT-111.25 m49″SingleCrimean Astrophysical Obs., Ukraine1981-
MPIA 1.21.23 m48.4″SingleWest Germany + SpainCalar Alto Obs., Spain1975-
Babelsberg Zeiss1.25 m49″SingleGermany, USSRBabelsberg Observatory; Berlin, Germany, Crimean Astrophysical Observatory 1924-
Galileo 122 cm1.22 m48″SingleItalyAsiago Observatory, Italy1942-
Samuel Oschin telescope1.22 m48″SchmidtUSAPalomar Observatory; California1948-
OHP 1.201.2 m48″SingleFranceHaute-Provence Obs., France1943-
Paris 48″ Reflector1.2 m48″FranceParis Observatory, France1871–1943-
Great Melbourne Telescope122 cm48″reflector – metalAustraliaMelbourne Observatory, Australia1878-1944-
Oskar-Lühning Telescope1.2 m47″SingleGermanyHamburg Observatory, Germany1975-
Leonhard Euler Telescope120 cm47″SingleSwitzerlandLa Silla, Chile1998-
Mercator Telescope120 cm47″SingleBelgium+SwitzerlandORM; La Palma, Canary Islands2001-
Hamburg Robotic Telescope 120 cm47″SingleGermanyHamburg-Bergdorf Obs., Germany2002*-
Hänssgen's reflector107 cm42″SingleGermanyMobile 2002*-
Grubb Parsons 40-inch102 cm40″SingleSwedenStockholm Observatory in Saltsjöbaden1930–present-
Nickel Telescope102 cm40″SingleUSALick Observatory, USA1979
Grubb 40-inch102 cm40"SingleUSSRCrimean Astrophysical Observatory Simeiz 1925–1944-
George Ritchey 40-inch 102 cm40″R/CUSAFlagstaff, Arizona 1934-
Yerkes "41-inch"102 cm40″SingleUSAYerkes Observatory, USA1968-
Meudon Observatory 1m100 cm39.4″SingleFranceMeudon Observatory/ Paris Observatory1891-
ZIMLAT100 cm39.4″SingleSwitzerlandZimmerwald Obs., Switzerland1997-
OGS Telescope100 cm39.4″SingleEuropean Space Agency countriesTeide Observatory, Tenerife 1995-
Jacobus Kapteyn Telescope100 cm39.4″SingleUK + NetherlandsIsaac Newton Group, Canary Islands1984
Lulin One-meter Telescope 100 cm39.4″SingleROC Lulin Observatory, Taiwan2002*-
Zeiss di Merate 100 cm39.4″SingleKingdom of ItalyMerate Obs., Merate, Italy1926
Zeiss 1m reflector100 cm39.4″SingleBelgiumRoyal Obs., Uccle, Belgium1920s-
Hamburg Spiegelteleskop'' 100 cm39.4″SingleDeutsches Reich Hamburg-Bergdorf Obs., Germany1911
1-m Carl Zeiss Jena100 cm39.4″SingleCCCPAssy-Turgen Observatory, Kazakhstan-
James Gregory Telescope94 cm37"SCTGreat BritainUniversity of St Andrews, UK1962
Schmidt 92/67 cm92 cm36″SchmidtItalyCima Ekar Observatory, Asiago, Italy 1966-
Kuiper Airborne Obs.91.4 cm36″SingleUSAC-141 1974–1995-
Stratoscope 291.4 cm36″SingleUSABalloon 1961–1973-
Crossley Reflector91.4 cm36″SingleUS+UKLick Observatory, USA1896
36-inch Yapp reflector91.44 cm36″ReflectorUKGreenwich & Herstmonceux1932

This table does not include all the 20th largest mirrors manufactured; the Steward Observatory Mirror Lab produced the 6.5-metre f/1.25 collimator used in the Large Optical Test and Integration Site of Lockheed Martin, used for vacuum optical testing of other telescopes.
Segmented are also known as Mosaic mirrors. Single mirrors, also called monolithic and can be sub-categorized in types, such as solid or honeycomb.

Selected telescopes with apertures of 90 cm (35.4 in.) and smaller

Some famous 20th century regionally famous telescopes, space telescopes, or otherwise significant.
NameAperture
m
Aper.
in
Mirror/typeNationality/SponsorsSiteBuilt/Used-
Hopkins Ultraviolet Telescope90 cm35.4″Single UVUSASTS, Earth Orbit1990, 1995-
Meudon Great Refractor83cm32.67"refractor FranceMeudon, France1891
83-cm Reflector, Toulouse Observatory83cm32.67"reflector-glassFranceToulouse, France1875
Focault 80 cm, Marseille Observatory80 cm31.5"reflector-glassFocaultMarseille, France1862-1965-
Astron80 cm31.5″Single UVCCCP + FranceEarth orbit1983–1989-
Potsdam Great Refractor 80 cm31.5 ″DoubletGermanyPotsdam, Germany1899
Ruisinger76.2 cm30″Single-NewtonianUnited States Louisburg, Kansas – Powell Obs.1985-
Greenwich 28 inch refractor
Royal Observatory, Greenwich
71 cm28″DoubletBritish EmpireGreenwich, England
Herstmonceux, England
1893
Meudon Great Refractor62 cmrefractor FranceMeudon, France1891
Infrared Space Observatory60 cm23.5″IR European Space AgencyEarth orbit 1995–1998-
IRAS57 cm22.44″R/C IRUS + UK + The NetherlandsEarth orbit1983
Mons Telescope50 cm19.7″SingleBelgiumTeide Observatory, Tenerife 1972-
Dutch Open Telescope 45 cm17.7″SolarDenmarkORM, Canary Islands1997-
Explorer 57 45 cm17.7″Single UVUS+UK+ESA CountriesEarth orbit 1978–1996-
Glazar UV telescope40 cm15.75″Single UVCCCPKvant-1, Earth Orbit1987–2001-
Glazar 2 UV telescope40 cm15.75″Single UVCCCP + SwitzerlandKristall, Earth Orbit1990–2001-
Mars Global SurveyorMOC35 cm13.8″R/CUSAMars Orbit1996–2006-
Griffith Observatory 12-inch Zeiss refractor30.5 cm12"AchromatUSAL.A., USA1931
XMM-NewtonUV camera30 cm11.9″Single UVESA CountriesEarth orbit1998-
TRACE30 cm11.9″Single EUV/UV/VisNASAEarth orbit1998–2010-
Hipparcos29 cm11.4″SchmidtEuropean Space AgencyEarth orbit 1989–1993-
Astronomical Netherlands Satellite22 cm8.7″Single UVNederlands & USAEarth Orbit1974–1976-
Galileo – Solid State Imager17.65 cm6.95″ReflectorUSAJupiter1989–2003-
Voyager 1/2, ISS-NAC17.6 cm6.92″CatadioptricUSASpace1977-
Spacelab IRT15.2 cm6″IR ESA + NASASTS, Earth Orbit1985-
Mariner 10 - TV Photo. 15 cm5.9″ReflectorUSASpace1973–1975-
Deep Space 1MICAS10 cm3.94″SingleUSASolar Orbit1998–2001-
Far Ultraviolet Camera/Spectrograph7.62 cm3″Schmidt UVUSALunar surface1972-
Voyager 1/2, ISS-WAC6 cm2.36″LensUSASpace1977-

At the end of the 20th century preliminary designs for Extremely large telescope of the 21st century were being worked on, as well as many smaller telescopes such as the Large Binocular Telescope

Under Construction

Examples of telescopes that were started in the 20th century, but may only have achieved a preliminary level of construction by the turn of the century.
Name/ObservatoryAperture
m
Aper.
in
Mirror typeNationality of SponsorsSite and/or ObservatoryFL or Built
GTC10.4 m409″Segmented,36Spain, Mexico, USARoque de los Muchachos Observatory, La Palma2007
Faulkes Telescope North2 m79″SingleUKHaleakala Observatory, Hawaii2003

Refractors