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Jacobus Kapteyn Telescope

WPC: Wide-field Photographic Camera

First light: March 1984.

De-commissioned: 1994.

Description: To take advantage of the high astrometric performance of the f/8 Harmer-Wynne optical system the JKT is provided with a wide-field photographic camera which provides an unvignetted field of 90 arc mins diameter on 250 × 200 mm plates. First light, the globular cluster M3 exposed for 60 minutes on unbaked unfiltered IIao plate by R. W. Argyle, took place on March 23/4 1984. The camera has an autoguider developed by D. Thorne very similar to those on the 2.5m telescope. The wide band filters are the same size as the plates and the useful field is inscribed to one end of the plate leaving the other end free for the plate number and sensitometer spots. The sensitometer is of the "Kitt Peak" design and shines light through the filter in use to the photographic plate. The camera is also provided with three fiducial lamps which expose small images on the plate which record the registration of the plate relative to the telescope. Thus the tangent point to the sky is known in principle which removes two degrees of freedom from astrometric reductions. Another novel feature of the camera is a roller shutter which always closes in the same sense as it opens so that all points on the plate receive equal exposure. The camera allows for nitrogen flushing so that the volume between the emulsion and filter is filled with dry nitrogen during the exposure, thus guarding hypersensitized plates against degradation.

The WPC can also be used in combination with fiber optics and CCD to image individual objects. This was first used by a group of astronomers from Leeds Astrophysics Group in 1987. They used a photograph as a template for placing fibre optics in the image plane of the JKT and fibres placed over the clear images of the stars. The positive plate with its fibres is replaced in the telescope, and the starlight disappears down the fibres as the telescope is aligned into its original position. Compared with other telescopes the JKT is very well suited to fibre optics. The Cassegrain focus accessible and rotatable unlike a Schmidt telescope.

Publications (scientific papers, technical publications, etc.).

Wide Field Camera manual

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Last modified: 22 August 2016