A multi-function day/night observation, ranging, and sighting device with active acquisition of optical targets includes a single objective lens and a single eyepiece lens and provides an image of a scene. The single objective lens leads to a visible-light first optical path and to an invisible-light second optical path. The invisible-light second optical path includes an image intensifier tube providing a visible image. The first and second optical paths converge with visible images provided by each pathway being overlaid at a reticule plane. A single light path leads from the reticule plane to the eyepiece lens. A laser provides pulses of laser light projected into the scene via the single objective lens, and the image intensifier tube is used as a detector for a portion of the laser light pulses reflected from an object in the scene in order to provide both a laser range finding function and an active optical target acquisition mode. The device includes a light-emitting display visible through the eyepiece lens providing ranging information superimposed over the image of the scene as seen by a user of the device. Methods of the device's operation are also disclosed.