Spotting scopes are small portable telescopes with added optics to present an erect image. They are used for birdwatching and other naturalist activities, such as hunting, verifying a marksman’s shots, surveillance, and for any other application that requires greater magnification than a pair of binoculars.
The light-gathering power and resolution of a spotting scope is determined by the diameter of the objective lens, typically between 50 and 80 mm (2.0 and 3.1 inches). The larger the objective, the larger the spotting scope.
The spotting scope optical tube has a small refracting objective lens, an image erecting system that uses either image erecting relay lenses or prisms and an eyepiece that is usually removable and interchangeable to give different magnifications. The eyepiece mount layout can be “straight” which means the eyepiece is on the same axis as the body of the scope, or “angled” meaning the eyepiece is at an angle of about 45 degrees to the body of the scope.