Optical Design Of An Image Degradation Reducing Enlarging Camera For The Prime Focus Of The Canada-France-Hawaii Telescope

E H Richardson

doi:10.1117/12.966191

9 January 1984 Optical Design Of An Image Degradation Reducing Enlarging Camera For The Prime Focus Of The Canada-France-Hawaii Telescope

E H Richardson

Author Affiliations +

Proceedings Volume 0445, Instrumentation in Astronomy V; (1984) https://doi.org/10.1117/12.966191
Event: 1983 Astronomy Conferences, 1983, London, United Kingdom

Abstract

To eliminate image motion and blur (caused by "seeing" effects of the Earth's atmosphere) it is necessary to introduce an optical system which produces a real image of the pupil (the primary mirror) followed by a reimaged portion of the field. For the Canada-France-Hawaii telescope (CFHT) at the prime focus, these optics are required to magnify the field from F/3.8 (which is the primary focal ratio of the telescope) to F/17 so that the electronic detector can adequately sample stellar images of 0.25 arcsec diameter. The image motion is removed at the pupil. A simple but wasteful method is to locate a shutter at the pupil which opens only when a guide star is in the mid position of its motion. The guide starlight is taken from the centre of the field before the light reaches the pupil and feeds an autoguider. An alternative is to locate a flat mirror at the pupil which is rapidly deflected to remove the seeing motion. Tests conducted by staff of the CFHT Corporation produced photographs showing 0.25 arcsec resolution using the prime focus corrector followed by an off-the-shelf lens. However this lens produced poor images off the centre of the 4 arcmin field within which the image motions might follow those of the guide star. Custom designed optical systems are described which produce sharp images over a wide spectral region and also provide the option of doing without the prime focus corrector resulting in higher transmission, less stray light and better resolution than in the trial arrangement.

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E H Richardson "Optical Design Of An Image Degradation Reducing Enlarging Camera For The Prime Focus Of The Canada-France-Hawaii Telescope", Proc. SPIE 0445, Instrumentation in Astronomy V, (9 January 1984); https://doi.org/10.1117/12.966191

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