Bird Spotting Scopes
A spotting scope is a compact telescope designed primarily for terrestrial observing and is used in applications which require magnifications beyond the range of a typical binocular. Compared to telescopes designed primarily for astronomy, a terrestrial telescope usually is designed with a shorter focal length for lower magnifications and wider fields of view and it has some type of erecting prism system to deliver a correctly oriented image to the viewer.
Spotting scopes are ideally suited for such activities as long distance birdwatching and nature study (shorebirds and raptors, for example), telephotography, scenic observing, long distance microscopy, beginning astronomy and surveillance. Depending on the type and design of the spotting scope, the useful magnification will range from about 10X to 250X, using either fixed or zoom eyepieces. The previous information presented on binoculars concerning magnification, aperture, focal length, field of view, exit pupil, eye relief, and light transmission is also true concerning spotting scopes, but because of the variability in optical design, these and other factors should be given further consideration.
Again, it's important to determine your primary use for the instrument as the optical design will directly affect its ability to perform under various conditions and its flexibility for different applications.
The sections listed above offer insightful advice on the factors to consider when buying a spotting scope.
Thanks to our friends at Eagle Optics for providing this information!