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The autoguider system in the Cassegrain A&G box cannot be employed when
the fibre system is used with ISIS, due to the size of the LARGEFEED
mirror.
The guiding system consists of three fibre bundles - two
semicoherent and one coherent - to carry the image of three stars to
a CCD camera. The image of the guide star, obtained with the coherent
bundle, can be use by the TV software to generate error signals for
the telescope control computer, in order
to improve the tracking of the telescope. This image and the two semi-coherent ones
can also be used for the set up of the telescope rotator
and for the acquisition of the field.
The guiding system includes:
- A coherent bundle manufactured by ORIEL; it covers a rectangular area
of 1.89 X 2.38 mm (8.5 X 10.7 arcsec on the sky). One half has a better
packing quality than the other half and, therefore, it is used to monitor
the object. The focal plane bundle end is connected to the aperture plate
via a connector. This connector has a pin to fix
the orientation (North) of the bundle. In order to group together the three
guiding
bundles, the other end of the coherent bundle was shaped to accommodate the
semi-coherent bundles.
- Two semi-coherent bundles 2.35 m long, each containing 15 fibres; the central
fibre and 6 ones in the first ring are of type FHP100/110/125 while the 8 fibres
in the second ring are of type FHP200/240/270. The 7 central fibres were
introduced in a polymide microtube of type PPC406/444. This group
covers an area of 1.6 arcsec on the sky. The second ring of fibres was
glued surrounding this microtube. In order to protect it, the whole structure
was inserted in a stainless steel tube of type 1100/1470. Each of the
semi-coherent bundles built this way covers an area of 4 arcsec
on the sky.
The orientation (North)
of each bundle is marked by a pin.
- A piece to group
the 3 guiding bundle ends when connected at the CCD camera. This can be rotated
and must be mounted at a certain orientation which is clearly marked.
- A Westinghouse ISEC TV camera.
- A lens relay system to produce the image of the guiding bundles on the
detector.
- A Melles Griot mechanical system for the manual focussing of the guiding
bundles
Next: Aperture plates
Up: The ISIS Fibre
Previous: The ISIS Fibre
Tue Aug 15 16:42:46 BST 1995