California Extremely Large Telescope
Encyclopedia
The California Extremely Large Telescope (CELT) was a proposal for an extremely large telescope
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 around 2003-4. The CELT was one of the earlier and more successful proposals for Extremely large telescope
s.
The optical design for CELT is a Ritchey-Chretien two-mirror system, with a segmented mirror
mosaic with 1080 segments. This rather naturally provides a large, 20 arcminute field of view
with less than 0.5 arcsecond images (100% enclosed energy). This focus is free of coma
and only suffers from astigmatism
, which grows quadratically with field angle. The primary will be 30 metres (98.4 ft) in diameter, and for compactness, the primary f-ratio
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 2.6 metres (8.5 ft) in diameter.
Extremely large telescope
An extremely large telescope is an astronomical observatory featuring a telescope with an aperture of more than 20 m diameter when discussing reflecting telescopes of optical wavelengths including ultraviolet , visible, and near infrared wavelengths. Among many planned capabilities, ELTs are...
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 around 2003-4. The CELT was one of the earlier and more successful proposals for Extremely large telescope
Extremely large telescope
An extremely large telescope is an astronomical observatory featuring a telescope with an aperture of more than 20 m diameter when discussing reflecting telescopes of optical wavelengths including ultraviolet , visible, and near infrared wavelengths. Among many planned capabilities, ELTs are...
s.
The optical design for CELT is a Ritchey-Chretien two-mirror system, with a segmented mirror
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 . They are used as objectives for large reflecting telescopes...
mosaic with 1080 segments. This rather naturally provides a large, 20 arcminute field of view
Field of view
The field of view is the extent of the observable world that is seen at any given moment....
with less than 0.5 arcsecond images (100% enclosed energy). This focus is free of coma
Coma (optics)
In optics , the coma in an optical system refers to aberration inherent to certain optical designs or due to imperfection in the lens or other components which results in off-axis point sources such as stars appearing distorted, appearing to have a tail like a comet...
and only suffers from astigmatism
Astigmatism
An optical system with astigmatism is one where rays that propagate in two perpendicular planes have different foci. If an optical system with astigmatism is used to form an image of a cross, the vertical and horizontal lines will be in sharp focus at two different distances...
, which grows quadratically with field angle. The primary will be 30 metres (98.4 ft) in diameter, and for compactness, the primary f-ratio
F-ratio
In oceanic biogeochemistry, the f-ratio is the fraction of total primary production fuelled by nitrate . This fraction is significant because it is assumed to be directly related to the sinking flux of organic marine snow from the surface ocean by the biological pump...
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 2.6 metres (8.5 ft) in diameter.