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The AAT prime focus and displaced observer (July 2000)

Tags: AAT, David Malin, astrophotography, photography, prime focus


When the Anglo-Australian Telescope was used to take conventional photographs the observer rode in the prime focus 'cage' at the top end of the telescope where light from the primary mirror is brought to a focus. This is shown in AAT 4a. However, since the mid 1990s, astronomical images began to be acquired with increasingly sophisticated electronic detectors known a CCDs (charge-coupled devices), and these have now completely replaced traditional photography.

These are larger and much more elaborate versions of the light detectors used in most digital cameras. They are now operated remotely from the telescope control room, or even from another location entirely, so there is no need (and no room!) for the observer to ride inside the 'cage' at all. Indeed for ease of access to the much more elaborate devices produced after the one pictured in 2000, the prime focus cage is a hinderance and has been removed. 

Credit: David Malin

© Australian Astronomical Observatory