Range finder devices can be classified into two types: active mode and active mode. In the active mode type, range finding light is projected onto an object and range finding is performed using reflection signal light. The passive mode type uses an image signal of the object. Active type range finders are widely used with compact cameras. An active range finder includes a light emitting unit having a light emitting element such as a light emitting diode (LED), a light emitting lens, a light receiving lens, and a light receiving unit having a light detecting element such as a position sensitive detector (PSD). The light emitting unit emits light toward an object through the light emitting lens, and the light receiving unit receives the light reflected from the object through the light receiving lens. Rangefinder instruments used on compact cameras make use of the infrared projecting, active autofocusing type trigonometrical range finding technique. Infrared light is projected from an infrared light-emitting diode (IRED) through a light projection lens on the object to be shot at or photographed, and the light reflected from the object is received by a semiconductor position sensor device (PSD) through a reception lens that is spaced away from the projection lens by a certain distance so that the distance of the object can be found by the position on which that reflected light is incident. The autofocusing device is used to find a shooting range for photographic camera or the like in automatic mode and to bring the objective into focus based on a result of the range finding and such autofocusing device allows everyone to enjoy photographing easily. Autofocus cameras are equipped with a rangefinder employing multiple flashes. Such a rangefinder comprises a plurality of light-emitting means emitting light to the subject, a light-receiving means that receives the light reflected from the subject for position detection, and an arithmetic processing unit which receives the output signal from the light-receiving means and calculates the distance to the subject. A light-emitting device and a light-receiving device are disposed at a given interval. The light-emitting device projects light onto the subject. The reflected light falls on the light-receiving device as a light spot. The distance to the subject is calculated on the principle of triangulation. In active type rangefinde cameras, a light-projecting section projects a beam toward an object to be measured (object to be photographed), the part of beam reflected by the object is received by a position sensitive detector (PSD) in a light-receiving section, and the distance to the object is measured (range-finding is effected) according to a signal outputted from the PSD. In operation, measured distance information is obtained by operating a light emitting element, emitting light to a photographed subject, detecting reflected light from the photographed subject and processing this reflected light. A distance from the camera to the photographed subject is detected by this measured distance information.

A laser rangefinder is device which can send out laser pulses and detect the returning pulses reflected from the target; the delay time of the pulses determines the target range. A laser range finder measures a distance to a target by a light flux having a predetermined wavelength. Laser based distance and range measuring equipment have been used for a number of years to provide extremely accurate distance measurements to a remote target or object. A laser rangefinder emits one or more laser pulses toward an object the range of which is to be determined. The laser pulses reflect from the object back to the rangefinder, and are detected by a laser detector. The length of time between emission of each laser pulse and its detection by the laser detector is measured by a timer clock, and the range is determined from this time period. Laser rangefinders consist of a laser which transmits of pulse of energy downrange toward a target. This pulse is reflected by the target and detected by the rangefinder. The round-trip delay of the return pulse is measured and used for the range calculation. A laser rangefinder also contains a sight unit for the operator to aim at the selected target. Laser rangefinders include a transmitter channel for transmitting a collimated light beam toward a target, a receiver channel for receiving and processing light reflected from the target, and an optical sighting channel through which the user could sight on the target. A typical flight time laser receiver typically comprises a low-noise detector/preamplifier, a differentiating stage, a time-programmed gain amplifier or time programmed threshold, and a comparator with a digital pulse output corresponding to the time of laser firing and the returned echo pulse signal. Laser range finder receivers generally rely on photodiodes for detection of target returns. There are two major categories of receiver photodiodes for detection: the acceptor intrinsic donor (PIN) diode, and the avalanche photodiode (APD). Either type of device can be based on indium gallium arsenide (InGaAs) or germanium technology. Generally, a laser transmitter is used to beam a high intensity pulse of light onto a selected target. The light scattered from the target is detected by an optical receiver which is normally located in close proximity to the laser transmitter. By measuring the transit time (flight time) between a transmitted laser pulse and the received echo, the range (distance) to the target can be determined using a time-interval counter. The flight time distance is calculated by such laser range finders by first measuring the elapsed time between the firing of a laser pulse at the target and the detection of the reflected pulse, then multiplying that elapsed time by the appropriate value of the speed of light.