The INO340 telescope is a Ritchey-Chrétien f/11 which provides unvignetted 20 arcmin filed of view at the main Cassegrain focus. In addition 3 bended focus are also provided each with a field of view of 8 arcmin. The primary mirror is meniscus shaped and the secondary mirror is convex and together they form a well-corrected focus.
|
Optical configuration |
Ritchey-Chrétien Cassegrain |
|
Wavelength range |
325-2500 nm |
|
Primary mirror diameter |
ID/OD (Nominal): 3400/700 mm |
|
Primary mirror focal ratio |
f/1.489 |
|
Exit focal ratio |
f/11.24 |
|
Entrance pupil location |
On primary |
|
Back focal distance |
1670 mm |
|
Unvignetted field of view diameter |
20’ |
The main mirror (M1) is single segment fast f/1.5 mirror with a diameter of 3.4m, which makes IN340 one of the most compact telescopes at this size. M1 is a meniscus shape 18 cm thick made of a Zerudor ceramic with a 700mm central hole. The M1 is polished to a surface micro-roughness of ~1nm root mean-squared, one of the thinnest in the world allowing short and long wavelength observations. The M1 is supported by 60 actuators which are actively or passively controlled to keep the mirror shape undistorted under its own gravity at different pointing.
|
Glass |
Ceramic ZERODUR® |
|
Shape |
Meniscus |
| mass |
~4000 kg |
|
Diameter |
3401 mm |
|
Optical diameter |
3300 mm |
|
Thickness |
180 mm ± 10 mm |
|
Central hole diameter |
700 ± 1 mm |
|
Radius of curvature (fronthyperbola) |
10200 ± 20 mm |
|
Radius of curvature (Rear face) |
10380 mm |
|
Focal ratio |
f/1.5 |
|
Surface roughness |
< 2 nm RMS |
|
Conic constant |
-1.006472 |
|
Scale |
0.18731 mm/arcsec |
The 600 mm secondary mirror reflects the light from the primary mirror and is also controlled by a hexapod positioning system that can move and tilt the secondary mirror in all degrees of freedom. The mirror has is made of a Zerodur ceramic and has a hyperbolic surface geometry. The mirror supports are active and can correct the shape of the mirror, for example correcting errors that may be caused by the changing zenith angle and temperature.
|
Glass |
Ceramic ZERODUR® |
|
Shape |
Convex |
|
mass |
~60 kg |
|
Diameter |
602 mm |
|
Optical diameter |
582.4 mm |
|
Thickness |
90 mm (center) |
|
Radius of curvature |
1812.4 mm ± 20 mm |
|
Surface roughness |
< 2 nm RMS |
|
Conic constant |
-1.7667 |
