The California Extremely Large Telescope (CELT) was a proposal for an

extremely large telescope The Extremely Large Telescope (ELT) is an astronomical observatory currently under construction. When completed, it is planned to be the world's largest optical/near-infrared extremely large telescope. Part of the European Southern Observator ...

design first proposed in the 1990s by a consortium of Californian Universities. The design was for a segmented 30 m diameter astronomical telescope. The CELT had a positive reception and continued to be developed, and was renamed the

Thirty Meter Telescope The Thirty Meter Telescope (TMT) is a planned extremely large telescope (ELT) that has become controversial due to its location on Mauna Kea, on the island of Hawaiʻi. The TMT would become the largest visible-light telescope on Mauna Kea. S ...

(TMT) around 2003–4. The CELT was one of the earlier and more successful proposals for extremely large telescopes. The optical design for CELT is a Ritchey-Chretien two-mirror system, with a

segmented mirror A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical or asymmetric (if they are part of a larger parabolic reflector). They are used as objectives for ...

mosaic with 1080 segments. This rather naturally provides a large, 20 arcminute

field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans a ...

with less than 0.5 arcsecond images (100% enclosed energy). This focus is free of

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

and only suffers from

astigmatism Astigmatism is a type of refractive error due to rotational asymmetry in the eye's refractive power. This results in distorted or blurred vision at any distance. Other symptoms can include eyestrain, headaches, and trouble driving at nig ...

, which grows quadratically with field angle. The primary was planned to be in diameter, and for compactness, the primary

f-number In optics, the f-number of an optical system such as a camera lens is the ratio of the system's focal length to the diameter of the entrance pupil ("clear aperture").Smith, Warren ''Modern Optical Engineering'', 4th Ed., 2007 McGraw-Hill ...

will be f/1.5. The final focus will be f/15, delivering a final focus with about 2 mm/arcsecond as its plate scale. Such a giant telescope produces very large seeing-limited images, a challenge for the design of seeing-limited scientific instruments. The 20 arcminute field is in diameter. CELT was one of three ELT projects that combined to start the TMT project. The other two projects were VLOT ( Very Large Optical Telescope) and GSMT ( Giant Segmented Mirror Telescope). Another large telescope proposal in this era was the Euro50 design.David Darling - extremely large telescope
/ref>

References

External links

CELT
website (archived)
California Extremely Large Telescope: Conceptual Design for a Thirty-Meter Telescope
Thirty Meter Telescope {{telescope-stub

See also

References

External links