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Published online by Cambridge University Press: 12 April 2016
The automatic star follower or autoguider described in this paper was designed for the Edinburgh 40/60 cm Schmidt camera. The stellar image in the focal plane of the 15 cm f/18 guide telescope is split optically to produce four stationary images which are sampled by a single image dissector tube, whose sequential output signals are proportional to the intensity of illumination in each quadrant. These signals are compared to produce error signals which are a measure of the radial displacement of the star. Guiding corrections in both right ascension and declination are applied to the fine motions of the Schmidt drive mechanism.
Measurements made on a typical plate given an exposure time of 30 min, and using guide stars down to magnitude 8.5 indicate a guiding accuracy of better than 0.14 arcsec or 2 μm at the focus of the guide telescope.