Telescopes and Techniques by C. R. Kitchin

Author:C. R. Kitchin
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

There remains one problem with the alt-az mounting, though: if an object is followed as it moves across the sky, the image plane rotates with respect to the telescope. For visual observing this field rotation is of little consequence, but when images are obtained with exposures of more than a minute or two, their outer edges will be blurred because each point there has become slightly trailed. The rate of field rotation varies in a complex manner with the position of the object in the sky and the latitude of the observer (three examples are shown in Fig. 6.4). With large telescopes on alt-az mountings the field rotation is countered by rotating the camera or other instrument in the opposite direction or by putting counter-rotating optical components, such as Dove prisms,1 into the beam of light before it reaches the focus.

Fig. 6.4The field rotation rates for alt-az-mounted telescopes for objects at declinations of 30°, 45°, and 60°, for an observer at a latitude of 45°N

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.