Field of View of Spotting Scopes
The widest dimension of circular viewing area observed through a telescope is the field of view. This is normally measured in linear feet at 1000 yards or in angular degrees. Since the field of view normally decreases with increasing magnification, this dimension will usually be smaller for a spotting scope than for a binocular, with a typical range of from 1 degree (52.5 feet) to 3 degrees (157 feet). Field of view is much more critical at close distances, so this range is quite adequate for the medium to long distance observation done with most spotting scopes. Except for a particular optical design (which will be discussed later) the near focus of a spotting scope is typically 20 to 30 feet.
Field of view is largely determined by eyepiece design. Some eyepieces are designed to deliver wide fields of view (wide angle) and these are very useful and popular for following a moving object, as in nature observation. Eyepieces designed for long eye relief generally have more narrow fields of view. Zoom eyepieces will usually have a more restricted field than an equivalent eyepiece of fixed focal length. Field of view can also be related to optical design as in the wide field characteristic of a telescope with a short focal length.
Thanks to our friends at Eagle Optics for providing this information!
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