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Last update: 26 Sep 2017
This page is designed by A.V. Moiseev
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The SCORPIO-2 project:
Spectral Camera with Optical Reducer for Photometric and Interferometric Observations - 2

The spectrograph layout

The multi-mode spectrograph SCORPIO-2 was developed using the experience of observations at the 6-m telescope BTA with the SCORPIO focal reducer. The new device is specialized for the large-format CCD EEV 42-90. It has a larger number of movable elements that is important for remote observations from the SAO RAS institute building. Also the opportunities for polarimetric observations are greatly expanded.

The optical layout includes two collimators (the main one and collimator for IFU mode), a camera and changeable elements: VPH-gratings, scanning Fabry-Perot interferometer, filters, analysers of polarization, phase plates. The total focal ratio at the primary focus of the 6-m telescope isF/2.6. The optical surfaces are coated with anti-reflective layers in the spectral range 3600-10 000 A. The anti-reflective coating were applied by Opto - Technological Laboratory (St. Petersburg).

The optics of the reducer compensates the aberrations of the main telescope mirror. SCORPIO-2 has 5 filter wheels for 10 positions in each for the changeable elements in the beam (filters, grisms, Wallaston prisms), a focal plane slide, a slide with analyzers of polarization, and a FPI holder.

The focal reducer consists of several units ('floors') mounted in the common case in the following order (from the telescope focal plane):

  • Floor 1: the focal plane slider on four positions (IFU enlargers, the long slit with the set of masks, the hole for direct images, the multi-slit unit). The slit width can be changed in the range 0.5-22''.
  • Floor 2: two filters wheels, the slider with rotated polaroid and phase plates (lambda/2, lambda/4)
  • Floor 3: the slider with collimators, a collimator focusing mechanism, the wheel with Wallaston prisms.
  • Floor 4: the grism wheel, the holder of FPI, a camera focusing mechanism.

Each floor has an independent microprocessor which controls corresponded motors. All microprocessors are operated by the prime focus computer using RS485 interface.


The SCORPIO-2 focal redcucer with open covers. The micrprocessors of floors 2 and 4 are seen.

The prime focus adapter

The focal reducer is connected with the platform-adapter which used for guiding by offset stars and for illumination the spectrograph by calibration lamps. The adapter contains two rectangular fields to search the guding stars. The centers of the fields are offset by 12' from the field of view center. A fiber bundle displaced by steps motors in a rectangular coordinate system is located in each of the field. The off-axis lens corrector in front of each guiding fields compensates the coma of the telescope primary mirror.

The optical design of the adapter contains the calibration optics, which forms a converging beam with the focal ratio equivalent to that of the telescope (F/4). It forms the output pupil of the calibration system in the same position with the image of the telescope mirros, which allows correct calibration of the wavelengths and flat-field. The entrance field of the calibration beam is illuminated via integrating Ulbricht sphere my two calibration lamps: with He-Ne-Ar filling for wavelength calibration and halogen lamp with continuos spectrum. The set of LEDs allows to create a desired curves of the spectral flat field.