The Coude Echelle Spectrographs (Expert Information)

Appendix C5: Telescope Setup for UHRF (night assistants)

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Aquisition TV

The UHRF aquisition TV (Pulnix CCD) is located slightly off axis back, towards the coudé 5 mirror. Since the Pulnix camera does not maintain focus with changing zoom, the zoom should be fixed for the night or if it is necessary to zoom out (for target aquisition) then the zoom should be returned to the same value.

Since the zoom is not encoded the following technique can be used to return to the original zoom value. When zoom and focus are first established, a fiducial mark should be placed in the centre of the square entrance hole on the slicer dekker. Bringing the hole back to this fiducial returns the original zoom.

Select ARC THAR and use its illumination to locate the slicer entrance aperture.

Pointing model

Since the UHRF entrance aperture is displaced from the centre of the UCLES slit by several cm, the UCLES pointing model is not entirely suitable for UHRF. Two CFUDGE offsets can be entered into the telescope CCS. Typical values in 1994 were -75, -46. UPDATE?


With the image slicer it is vital that LAMBDA offsets be used, by issuing the LAMBDA command to the telescope computer control system (CCS). This takes a few seconds to move the star; be patient.

The LAMBDA correction should be revised at the end of each exposure by setting LAMBDA 5500 Å recentering the star on the slicer aperture, and then issuing LAMBDA lambda again (where lambda is the wavelength of the observation).

TV guiding is straightforward. Use the CCS TVCR command. The SS1 and SS2 lights should be off and the SS3 light on.

Ray Stathakis (
Last Update: 22 March 2000