Open Access
Table 1
Telescope parameters for the three telescopes (Cayrel 2012; Nelson & Sanders 2006; Bernstein et al. 2014).
| Telescope parameters | ELT | TMT | GMT |
|---|---|---|---|
| Field of view (arc minutes) | 10 | 15 | 20 |
| Wavelength of operation (µm) | 0.32–25 | 0.32–28 | 0.32–25 |
| Primary mirror-M1 | Elliptical concave | Hyperbolic concave | Elliptical concave |
| Diameter (m) | 39 | 30 | 25 |
| Conic constant | −0.996 | −1.00097 | −0.998 |
| Segment type | Quasi hexagonal | Quasi hexagonal | Circular |
| Segment size (m) | 1.45 | 1.44 | 8.365 |
| Segment gap | 4mm | 2.5 mm | 0.345m |
| Number of segments | 798 | 492 | 7 |
| Secondary mirror-M2 | Hyperbolic convex | Hyperbolic convex | Elliptical concave |
| Diameter (m) | 4.1 | 3.1 | 1.05 |
| Conic constant | −2.28962 | −1.381 | −0.716927274 |
| Segments | No | No | Yes |
| Number of Segments | NA | NA | 7 |
| Active/adaptive control | Yes | No | Yes |
| Tertiary mirror-M3 | Circular concave | Flat | Flat |
| Diameter (m) | 4 | 3.5×2.5 | 0.3 |
| Inclined angle (°) | 0 | 45 | 45 |
| Quaternary mirror-M4 | Flat | NA | NA |
| Diameter | 2.38×2.34 | ||
| Inclined angle (°) | 7.25 | ||
| Fifth mirror – M5 | Flat | NA | NA |
| Diameter | 2.6×2.1 | ||
| Inclined angle (°) | 37.25 | ||
| Proposed coating | Protected Silver | Protected Silver | Bare aluminum |
| Final focal ratio | f/17.48 | f/15 | f/8.2 |
| Instrument mounting locations | Nasmyth platforms A and B | Nasmyth platforms A and B | Direct Gregorian Folded port Auxiliary ports |
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