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Spotting scopes are compact telescopes designed primarily for terrestrial observing and 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.
Magnification (Power)
Spotting scopes are often referred to by two numbers separated by an "x". For example: 15-45x60. The first number is the power or magnification of the spotting scope. With a 15-45x60 variable power spotting scope, the object being viewed appears to be 15-45 times closer than you would see it with the unaided eye. The magnification of target scopes is typically on the order of 20X to 60X.
The light gathering power of spotting scopes is determined by the width of the objective lens. All else being equal, the larger the objective, the more heavy and expensive the spotting scope.
There are three types of target scopes:
- Straight-through - the eyepiece is on the same axis as the body of the scope
- Angled - the eyepiece is at an angle of about 45 degrees to the body of the spotting scope
- Shoulder-mounted - rare design, more complex
Straight through spotting scopes are easier to use from, say, inside a car, while angled target scopes are more comfortable for tall people and more easily shared by people of different heights.
The choice of the eyepiece lens determines the overall magnification. The best magnification is decided by a number of factors. Magnifications of less than 20X are unusual, mostly due to the fact that binoculars and monocular provide this magnification.
Spotting scopes can be used for variety of activities. For bird watching, 20X or 30 is typically favored. Among aircraft spotters, the term "pole" is used as a shorthand expression meaning telescope. The related verb "to pole-off" therefore means reading some identication marks of an aeroplane by using telescope.
Target scopes are available for day or night time viewing. Among the more popular are Bushnell scopes and ATN scopes.
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