Previous: Guide fibre bundle focussing
Up: Installation and Setup for Fibre observing
Previous Page: Guide fibre bundle focussing
Next Page: Setting up FOS

Spectrograph set up

The spectrograph setup procedures for long slit observing are described above. The plane and tilt of the fibre slit can in principle be different from those of the long slit, the difference in the plane of the slits causes a difference of the distances from the fibre and long slits to two collimators. Because spatial resolution is important, the spectrograph should be set up to provide a collimated beam onto the grating. The nominal values of the collimator settings for long slit observing to provide such a situation are 7000 microns for the Blue arm, and 9000 microns for the red arm. The procedure to ensure that the spectrograph is correctly set up for fibre observing is as follows:-

• With the slit unit in the long slit position, set the two collimators to their nominal values.
• Ensure that the spectrograph can be focussed with the collimators near these values, by making adjustments to the capstans on the CCD cryostats, as described in Section 8.3.2.
• Ensure that the tilts of the focal planes are correct, again by adjusting the capstans as described in Section 8.3.2.
• Ensure that the rotation of the CCDs is such as to align the long axis of the chip with the dispersion direction, again as described in Section 8.3.1.
• Move the slit carriage to the multislit position with the command MSLIT, and remove the Acquisition and Comparison mirror.
• Switch on the fibre calibration lamp.
• Using the Hartmann procedures, focus the spectral lines from the fibres onto the CCDs by moving the collimators.
• Correct for any residual tilt along the fibre slit by making balanced moved of the CCD capstans, i.e always keeping the centre of the focal plane in the same case.

The difference between the collimator position for best focus for the long slit and for the fibres should be the same, and of the same sign, for both red and blue arms.