A rangefinder is a device that measures distances remotely. Optical rangefinder has two objectives .- a known fixed distance apart (base). With them points to an object until the image from the two objects overlap into one. The range finder calculates the distance to the object from the base length and the angles subtended between the axis of the objectives and the base line. The higher the base line, the more accurate rangefinder. Morphic rangefinders are based on calculations using trigonometry and have been used in targeting systems for firearms, surveying and photography, to help focus. .- The ultrasonic range finder based on a completely different principle. The rangefinder emits an ultrasound that is reflected in the target and the rangefinder receives the echo. For the time and phase of the echo, calculates the distance to the target. You can find this type of rangefinder cameras in some "Polaroid". Laser rangefinder .- The laser rangefinder is able to perform distance measurements automatically as ultrasound, but with greater accuracy than optical rangefinder. This is because the laser is reflected in a very small area of ​​the target and is modular so you can combine the two previous techniques.