Many different technologies are used with optical range finders. One simple type of instrument operates on the function of triangles. When the operator looks through the eyepiece, when the instrument is not set for the distance, they will see two identical images. The operator adjusts the focus until two images are in coincidence, superimposed on top of each other. The distance is read from a scale on the instrument. Optical range finders have an acceptable level of accuracy for reconnaissance or sketching purposes for short distances, but the error increases as the distance increases.
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