A spotting scope is a portable telescope, optimized for the observation of terrestrial objects. The magnification of a spotting scope is typically on the order of 20X to 60X. Other common features include:
The light gathering power of a spotting scope is determined by the width of the objective lens, typically between 55 and 80 mm. All else being equal, the larger the objective, the more heavy and expensive the telescope.
There are three types of scope: "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 scope), and, rarely, a more complex, shoulder-mounted design. Straight-through scopes are easier to use from inside a vehicle while angled 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, as (much cheaper and lighter) binoculars or monoculars can provide this. Magnifications of more than 60X lead to poorer brightness and, even on a tripod, shake can be a problem. The field of view is also limited.
Usually for birdwatching, but spotting scopes are popular when used in longrange hunting mounted on a lightweight hunting tripods. 20X or 30X are favoured for birdwatching. 20x-60x variable powers are used for longrange hunting if combined with solid mounting platforms. This gives a good field of view and a bright image. Spotting scopes are also used on many target ranges to avoid walking to the target to verify the placement of hits.
Amongst aircraft spotters the term "pole" is used as a shorthand expression meaning telescope. The related verb "to pole-off" therefore means reading some identification marks of an aeroplane by using a telescope. Other users might employ the same slang term.
Spotting scope manufacturers fall into several groups. At the top end of the market, it is generally accepted that three manufacturers compete strongly for the ultimate in quality: Swarovski are the most expensive of all, closely followed by Leica, and Zeiss. Several manufacturers produce scopes that are generally thought to be of almost equal quality to the top three, but at about half the price, among them Kowa, Nikon, and Pentax.