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Lightweight Laser Designator Rangefinder, laserowy dalmierz

A rangefinder (also rangefinding telemeter, depending on the context) is a device used to measure distances to remote objects. Originally optical devices used in

surveying Surveying or land surveying is the technique, profession, art, and science of determining the terrestrial two-dimensional or three-dimensional positions of points and the distances and angles between them. A land surveying professional is ca ...

, they soon found applications in other fields, such as photography and in the military. They were specially useful for finding the range of a target, such as in naval gunnery and

anti-aircraft artillery Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...

. The word ''telemeter'' is derived .

Designs

The first rangefinder telemeter was invented by

James Watt James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was fun ...

in 1769 and put to use in 1771 in surveying canals. Watt called his instrument a micrometer, a term now used with a different meaning in engineering (the

micrometer screw gauge A micrometer, sometimes known as a micrometer screw gauge, is a device incorporating a calibrated screw widely used for accurate measurement of components in mechanical engineering and machining as well as most mechanical trades, along with ot ...

). It consisted of two parallel hairs in the focal plane of a telescope eyepiece crossing an upright hair. At the point to be measured, two sliding targets on a surveyor's rod were adjusted to align with the hairs in the telescope. The distance to the rod could then be determined from the distance between the targets on the rod by trigonometry. Several others have been credited with the invention of the rangefinder telemeter at one time or another. The

Royal Society of Arts The Royal Society for the Encouragement of Arts, Manufactures and Commerce (RSA), also known as the Royal Society of Arts, is a London-based organisation committed to finding practical solutions to social challenges. The RSA acronym is used m ...

gave an award to W. Green for its invention in 1778, even though they were made aware of Watt's priority. In 1778,

Georg Friedrich Brander Georg Friedrich Brander (* 28. November 1713 in Regensburg; † 1. April 1783 in Augsburg) was an important maker of scientific instruments. Early years Brander was born 1713 to Georg Brandner, an apothecary with roots in Nuremberg, and Sibylla ...

invented the coincidence rangefinder. Two mirrors set a distance apart horizontally in a long slim box, similar to a

subtense bar Tacheometry (; from Greek for "quick measure") is a system of rapid surveying, by which the horizontal and vertical positions of points on the earth's surface relative to one another are determined without using a chain or tape, or a separate le ...

but located at the measuring station, and forming two images. This rangefinder does not require a measuring rod at the target and could perhaps be considered the first true telemeter. In 1790 Jesse Ramsden invented a half-image range finder. Though

Alexander Selligue Alexander François Selligue (1784-1845) was a French engineer. His name was in fact Alexandre François Gilles, but he used Selligue as an anagram of Gilles. In 1832, he together with David Blum patented an application of shale oil for direct il ...

is often mistakenly credited with the invention, he did invent an improved telemeter with fixed lenses in 1821 and is responsible for coining the term. In 1899, Carl Pulfrich at Carl Zeiss AG fabricated a practical stereoscopic rangefinder, based on a patent of Hector Alexander de Grousilliers. World War II era telemeters worked optically with two telescopes focused on the same target but a distance apart along a baseline. The range to the target is found by measuring the difference in bearing of the two telescopes and solving the skinny triangle. Solutions can be obtained automatically, using tables or, rarely, manual calculation. The greater the distance to the target, the longer the baseline needs to be for accurate measurement. The baseline required for the telemeters for battleship guns is very large. More modern telemeters use an electronic technology such as lasers or radar.

Applications

Applications include

, navigation, to assist focusing in photography, choosing a golf club according to distance, and correcting aim of a projectile weapon for distance.

Golf

Laser rangefinder A laser rangefinder, also known as a laser telemeter, is a rangefinder that uses a laser beam to determine the distance to an object. The most common form of laser rangefinder operates on the time of flight principle by sending a laser pulse in ...

s are used in golf to measure the yardage of a particular shot but also to gauge slope and wind as well. There has been debate over whether they should be allowed in tournaments. While their use is banned on the professional level, they are becoming widely used on the amateur level.

Ballistics

Rangefinders may be used by users of

firearm A firearm is any type of gun designed to be readily carried and used by an individual. The term is legally defined further in different countries (see Legal definitions). The first firearms originated in 10th-century China, when bamboo tubes ...

s over long distances, to measure the distance to a target to allow for projectile drop. Until the development of electronic means of measuring range during the Second World War, warships used very large optical rangefinders—with a baseline of many meters—to measure range for naval gunnery.

Forestry

Rangefinders are used for surveying in forestry. Special devices with anti-leaf filters are used.

Virtual reality

Since the 1990s, rangefinders have been used in virtual reality systems to detect operator movements and locate objects.Kidd, Cory D. ''et al.'' (1999) "The aware home: A living laboratory for ubiquitous computing research" ''Lecture Notes in Computer Science'' 1670: pp. 191–198,

References

External links

{{Commonscat, Rangefinders
Rangefinder Comparison - A National Forest Service document
Length, distance, or range measuring devices