A schematic representation of the acquisition unit is shown in Figure 3.
A coherent fibre bundle transports light from the focal plane (via the SP) to a standard TV camera. Figure 4 indicates where this bundle is connected into the SP. It has a field of view of 22.5 30.2 arcsec in the telescope focal plane.
Figure 3: Acquisition system. The focussing mechanism is at bottom-left of the main unit
The acquisition system is equipped with a filter wheel which can accommodate up to six filters. The filters must be circular and 25mm in diameter. In the standard configuration the following filters are provided: CLEAR, BG38, GG495, OG530, and RG630.
A lens (with magnification 1:1.5) forms the image of the bundle output over the chip of the TV camera.
The TV acquisition system consists of a Westinghouse ISEC TV camera connected to the TV camera controller, a VME camera microprocessing system, a display monitor, and the control terminal.
Figure 4: View of relevant regions/components at the telescope focal plane area. On the Swing Plate all possible bundle mount points are marked along with those currently used (the standard positions for bundles 1, 2, and 3 - code 3, 4, and 2 respectively). The acquisition bundle location is also shown. The rectangular shaded areas illustrate the available region for guiding, which can be scanned by the two coherent bundles. Numbers in the table indicate the coordinates of the extremes of this region. The circular shaded area represents the region which can be illuminated by the calibration lamp. This orientation corresponds to a view from the GHRIL table at Sky Position Angle (SPA) = 0 degrees. Therefore, North is Top.