Range-finding instruments are used to determine how far an object or target is from the position of the rangefinder. The technical principles upon which optical rangefinders are based were first developed during the late 1700s by French astronomer Alexis Marie Rochon. Although they may vary slightly, all optical designs are based upon simple trigonometry. They formulate distances by using a system of lenses and mirrors to establish and measure angles. Through the years, scientific breakthroughs have greatly improved rangefinder precision and accuracy. Most of today's rangefinders utilize high-tech electronics and have found uses in many fields.
Today, due to advances in laser and digital technology, small handheld digital rangefinders can easily go anyplace where precise distance calculations are needed. Laser rangefinders calculate distance by two methods: by measuring the time it takes for a narrow-band laser pulse to travel to and from the target, or by light wave interferometry, which measures the degree of wavelength interference. Because of convenience, precision, and accuracy, the laser rangefinder has become by far the most preferred method of distance determination among both sportsmen and professionals. Below are a few examples of its usefulness and versatility:
In this age of technology, optical rangefinders still make great backup systems for hunters who can't chance a second shot due to a dead battery, or professionals who can't afford lost time because of technical difficulties. They're durable, accurate, and weather-resistant, and best of all, they don't need batteries. These early rangefinders found immediate practical application in the field of photography and were widely used up until the late 1950s before being replaced by the introduction of the single-lens reflex camera (SLR). They were the first types of rangefinders to be adapted for military weapons, and also greatly improved modern surveying techniques.
In addition to laser and optical rangefinders, fishermen have found that sonar rangefinders, also called fish locators, are the best way to pinpoint the depth and location of hidden fish. The unique ability of water to conduct sound waves has made sonar the most accurate way to calculate underwater speeds and distances.