90 cm Telescope

Mechanical characteristics

Optical characteristics

Other characteristics

Accuracy, pointing, speeds and auto-track camera.


Mechanical characteristics

Mounting: equatorial (37º 4m)
Structure: steel and welded iron
Weight: 24 Tm
Polar adjustment: screw

  • Latitude, better than 1º
  • Azimuth, better than 1,5º
  • Lowest resonant frequency: > 5Hz

Right Ascension axis

The Right Ascension axis is fork type. The rear of the axis is mounted on a preloaded ball bearing. The main suspension consists of a spherical section supported by oil-pads to allow almost friction free rotation.
Rotating weight: 16 Tm
Inertia: 5060 kgm²
Bearing: 1 preloaded ball
Sphere: 1,2 m
Oil-pads: 2
Oil film thickness: 80 mm ± 10 mm
Friction: 4,5 kpm
Angle of rotation: ± 180o Mechanical limit: none
Electrical limit: two software and two hardware limits
Gears: two identical and diametrically opposed
Drive ratio: AR 360:1
Brakes: two on the motor axes
Motors: two Inland-T-5745D
Tachometer: none
Codificadores angulares:

  • 1 relative 72000CC Heidenhain-ROD230 in the motor axis.
  • 1 absolute (10 bits-Gray) with gearing of 1:1 in the RA axis.
  • 1 relative Inductosyn with 1" directly in the RA axis.


For mounting of several instruments.

  • 1 along the lenght of the fork.
  • 2 across the fork.

Declination axis

This consists of a central cubic block and two Serrurier structures, one large and one small to support the secondary and primary mirrors respectively. At the sides of this cube are two hollow tubes for connection to the fork by means of preloaded ball bearing. At the end of each of these tubes are located the instrument planes.
Inertia: 950 kgm²
Bearing: two preloaded balls
Friction: 3,0 kpm
Angle of rotation: 120o
Mechanical limit: the fork
Electrical limit: two software limits, two hardware limits and one mercury switch limit with the revolution simetry
Gears: two identical and 120º apart
Relación motor: DEC 360:1
Brakes: two electromagnetics brakes on the motor axes
Motors: two Inland-T-5745D
Tachometer: None
Angle encoders:

  • 1 relative 72000CC Heidenhain-ROD230 in the motor axis
  • 1 absolute (10 bits-Gray) with gearing of 1:1 in the DE axis.
  • 1 relative Inductosyn with 1" directly in the RA axis.

Primary assembly

The primary mirror is held in the assembly by a series of fixed supports and counterbalance weights in both axial and radial planes. The mirror is aligned by a dowel located at the centre of the assembly. Adjustment of the lateral counterweights relieves excessive forces on the central dowel. The three fixed supports are for adjustment of the inclination of the mirror.
Weight: 0,58 Tm
Fixed axial supports: 3 (screws)
Axial counterbalance weights: 3
Radial counterbalance weights: 8
Segurity limits: 4

Secundary assembly (Focus)

The secondary mirror is suspended in the secondary assembly by four steel adjustable arms with screw adjustments for centralising and inclination. These allow adjustment over the axial axis.
Weight: 105 kg
Adjustment: 22 mm
Motor: stepping motor HY-200-2220-100-A8 with reduction gears 40:1
Lineal encoder: LVDT Schaevitz-500-DC-D type
Minimum step: 12mm±3@120mm in the focal plane

Tertiary assembly

The tertiary assembly is suspended from a cube by a spider and is aligned with screw adjusters for height and inclination. Inside the cube are the supports for the tertiary mirror with a tilting mechanism that allows the optical path to be directed at both foci. There are two locking screws to give the necessary precision for repeatability.
Weight: 130 kg
Adjustment: ± 47º
End stop: mechanical and electrical
Drive: cable and spring tensioner
Motor: stepping motor HY-200-2220-100-A8 with reduction gear

Instrument mounting plane(P.A.I.)

There are two planes for instrument mounting, east and west, consisting of circular plates 500 mm in diameter. Mounting is accommodated by six M10 tapped holes located 60o apart on a 350 mm diameter.
Maximum diameter: 500 mm
Internal diameter: 300 mm
Diameter of optical aperture: 90 mm
Fixing: M10 x 6 a Æ F 350 mm
Sighting telescope:

  • Type: Cassegrain
  • Aperture: 120 mm
  • Focal relationship: f/12,5
  • Field: 50´
  • Intensified camera: EEV
  • Field of camera: 18´x 13´

Optical characteristics


General Characteristics

Aperture 0.9 m
f/# 8
Focal distance 7200 mm
Scale 35 μm/" (28.65 "/mm)
Clear field of view 26,4' (55.4 mm)
Spectral range Visible
Configuration Ritchey-Chrétien
Number of foci 2 (Nasmyth)
Primary - secundario distance 1540 mm
Secundary - tertiary distance 1140 mm
Tertiary - Instrument adapter plane 1104 mm
Instrument adapter plane - main focus 221 mm
Focal ragne (From the instrument adapter plane) 110 - 330 mm


Primary mirror

External diameter 910 mm
Diamter of the central hole 104 mm
Thickness of the border 123 mm
Ratio of diameter to border thickness 7.4
Radius of curvature 4680 mm
Conical constant (e2) 1.11
f/# 2.6
Material K4
Weight 180 kg


Secundary mirror

External diameter 326.7 mm
Diamter of the central hole 96.6 mm
Thickness of the border 48.1 mm
Ratio of diameter to border thickness 6.8
Radius of curvature 2369 mm
Conical constant (e2) 4.9
f/# 3.63
Material V02
Weight 10 kg


Tertiary mirror

Form Octogonal
Main axis 295 mm
Minor axis 215 mm
Thickness of the border 50 mm
Ratio of main axis to border thickness 5.9
Material V02
Weight 8 kg



The observatory has an operational reflectometer since January 2010. In Reflectivity T90 page can see graphically a record of the mesurements of reflectivity as well as of scattering for each one of the mirrors belong to the T90 telescope.


Other characteristics

Accuracy: better than 1" in 1m

Pointing without correction: better than 40"

Speeds: 1.5°/ss, 20´/ss, 2´/ss

Auto-track camera:

DARK-STAR fitting in the visor of the Strömgren diaphragm.