Long-range optics encompasses optical systems for terrestrial or astronomical purposes. They enlarge far-away objects to make details visible to the human eye. These devices are used for astronomical observation and wildlife spotting as well as for sports activities.
Astronomy is the science of heavenly bodies. Telescopes are used in order to observe these closely. Telescopes are optical devices equipped with enlarging lenses, prisms and mirrors. The purpose of a telescope is to enlarge the visual angle and thus to increase the resolution of the visual system when observing distant objects. The first telescopes used two lenses, a collecting objective and an eyepiece or ocular lens. The Dutch or Galilean telescope is considered the forerunner of later telescopes. It possesses a divergent eyepiece lens, in contrast to the astronomical or Keplerian telescopes with their collecting eyepiece lenses that were developed later.
Binoculars, field glasses or binocular telescopes are compact pairs of telescopes. In general, telescopes with a binocular design make it possible to observe objects through separate optical paths. Prism binoculars are based on the principle of Keplerian telescopes and contain an erecting prism system between the eyepiece and the objective lens that rectifies the inverted image and enables designs yielding high quality images to remain compact. Opera glasses are small pairs of binoculars intended for use in theatres or concert halls. These small and lightweight binoculars work in the same way as Galilean telescopes. This means that they contain a convex objective lens and a concave eyepiece lens. Since this combination creates an upright image directly, reversing optics are not required. When designed for use with one eye only, the result is termed a monocular. Various other telescopes are available for use in a range of applications. Hunters value high-quality optical performance and robust, weatherproof casings. Those interested in observing birds and animals value colour accuracy and sharp images that facilitate the perception of details. Minimising weight and size is important when binoculars or telescopes are intended for use during leisure activities like mountain tours or hikes, or while on holiday.