Field of viewThe width of the picture seen through a pair of binoculars or a telescope, expressed as a segment in degrees or, more usually, as so many metres at a distance of 1,000 metres. The higher the magnification the smaller the field of view will be if the size and weight of the instrument are to be kept within reasonable limits.
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver