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Introduction to the CCD system

The camera system - shown in figure 4.3 - consists of the following parts:

• The liquid nitrogen cooled camera head which is mounted at the appropriate spectrograph focus.

• The analogue drive box which is mounted within about 2 metres of the camera head.

• The digital controller which is located off the telescope and interfaced to the instrument computer. For data collection the instrument computer uses a disk (and tape) with Lexidata display.

The camera head is an evacuated cryostat which supports (and cools) the CCD behind an anti-reflection coated fused silica window. A preamplifier and temperature controller are attached to the cryostat. There are no moving parts, except the three-point kinematic mount which provides focus and tilt adjustment manually. The drive box contains CCD clock drivers, analogue-digital conversion and associated electronics.

The controller box is programmable via the instrument computer to define the particular mode of operation of the camera; it is linked via a CAMAC module to the Instrument Computer. No electronic adjustments should normally be necessary to the camera system.

Details of camera set-up and routine observations are given in the following sections.

• CCD format
• Signal levels, noise and dynamic range
• Preflashing