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Auxiliary Focus Imaging

The Auxiliary focus is a facility provided in the Cassegrain A&G box to allow a direct image to be taken on-axis at the Cassegrain focus, at the expense of an extra (45 tex2html_wrap_inline5509 ) reflection. The original idea of the system was that it could be used for short direct images of objects which were part of a mainly spectroscopic programme, but it has emerged as the major instrument for a number of projects for which the high throughput in the ultraviolet provided by an all-reflecting optical system, or the 0.1 arcsec pixel size, are a particular advantage. The image quality at Cassegrain is illustrated by Figure  4 which shows spot diagrams for this focus.

Figure 4: Spot diagrams for the WHT Cassegrain Focus

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Wed Sep 17 12:36:20 BST 1997