optical system is particularly suitable to be included in an optical sight unit and for purposes of explanation only the present invention will be described in conjunction with an optical sight the task of such a sighting assembly is to point at follow a target and while also collecting the radiation emitted by a movable object in order to compare the trajectory of the movable with the line of sight and determine the deviation between them the manner of how the measuring operation is performed is immaterial to the operation of the present invention nevertheless the deviation determined by the measuring operation is converted into an electrical signal and how this signal is processed and evaluated is immaterial to the operation of the present invention the optical system forming the present invention includes a single entrance aperture with an objective lens 1 a glass plate 2 and a prism 3 to split up the visual light from the target and its background and the radiation emitted by the radiation source of the object the radiation source may for instance consist of a laser source preferably a laser diode disposed on the object in such a way that laser radiation is transmitted towards the optical system the objective lens 1 collects both visual light and laser radiation and is designed in such a way that the focal distance for visual light and diode laser radiation is different from this it directly follows that an image of the target and its background is projected in the image plane f 1 for visual.