Apparatus and method of investigating surface properties

A method of investigating optical surface properties of a layer of paint, wherein light is radiated by means of a light source through an opening in an optic block onto a surface to be investigated and the light reflected and/or scattered by the surface as a consequence of this radiation is detected with a first detector device at a first pre-set angle with respect to the light beam radiated from the light source onto the surface, is detected with a second detector device at a second pre-set angle with respect to the light beam radiated from the light source onto the surface and is preferably detected by means of a third detector device at a third pre-set angle with respect to the light beam radiated from the light source onto the surface, wherein, while the method is carried out, at least two filter elements with mutually different optical properties, which are arranged on a common carrier movable with respect to the light source, are brought into a beam path between the light source and the surface in a manner staggered in time, so that only one filter element is present in this beam path in each case, and wherein a beam splitter device is positioned between the surface and at least one detector device of the first through third detector devices, the beam splitter device having a single input for decoupling a portion of the light scattered off or reflected from the surface, and two outputs including a first output of the two outputs to an integral color measurement detector of the first through third detector devices and a second output of the two outputs to an imaging sensor.