Astronomical Institute AS CR Academy of Sciences CR
Astronomical Institute,
Academy of Sciences of the Czech Republic

Coudé Spectrograph

Single order coude spectrograph working in the first and second spectral orders.

schema of coude

Description of the spectrograph

  • Separating glass plate - the glass plate is installed in the tube connecting the coude room to the telescope. This tube is corresponding to the hour axis of the telescope. The ligh beam is going through this tube to the slit head. The glass plate divides space in coude room and the dome and thus it prevent from the draught.
  • Turning prism + eyepiece - in principle, the astronomer should be able to look to the field of vision of the telescope (although we do not use it very often). Then one can put a prism to the optical path and redirect the light beam to the ocular with thread cross.
  • Dichroic mirrors - we have 4 dichroic mirror for the optimal separation of spectral orders: red, infrared, blue and aluminium. However the profit is not very important and thus, mainly due to autoguiding (see individual chapter in link bellow) we use aluminium mirror.
  • Slit - 0.2mm (0.6arcseconds).
  • Exposuremeter: just behind the slit, semitranslucent mirror, about 5% of the light to the exposuremeter.
  • Spectral filters - for the separation of spectral orders.
  • Collimator - focal ratio 1:32, out of axis.
  • Grating - works in the first and second spectral orders.
  • Schmidt camera (correction plate + spherical mirror)
  • Detector

Slit head

  • Flat field lamp: Hollow cathode
  • Comparison light: ThAr lamp, 15mA
  • Slitwidth: 0.2mm (0.6arcsec)
  • Spectral filters: to separate spectral orders

    Numbercolortyprange (A)
    1empty hole  
    2red 1RG26350 - 7910
    3red 2OG44800 - 9000
    4determalC9971< 6000
    5blueBG393500 - 5500

    For the first spectral order (red) we do not use any filter (number 1 - empty hole), for the second spectral order (blue) we use filter number 5.

    Grating, spectral resolution, spectral orders

    • Producer: Bausch and Lomb
    • Grating: 833.17 gr. per mm
    • Resolving power: about 13000 in Halpha
    • Spectral orders:
      1: cca 5100A - 9100A
      2: cca 3700A - 5100A


Schmidt camera, focal length 700mm


  • Type:Pylon Excelon,
  • dimensions: 2048x512 pixels, one pixel dimension: 13.5micrometer
  • chip ID E2V 42-10 BX
  • cooling: liquid nitrogen, work temperature -115 C
  • zero level signal (bias) 600.2 ADU
  • saturation 65535
Last update 17.2.2015