The invention relates to a device for detecting diffusely scattered impurities (18) in receptacles (10) with a transparent wall (16). The inventive device has a light source (12) producing one or several beams of light (14) to illuminate said wall (16) and also comprises an optical detector (22) producing an image of the illuminated wall (16), wherein the light source (12) and the optical detector (22) are arranged according to dark-field detection. The light source (12) is configured in such a way that the intensity of the light beam(s) (14) emitted therefrom is distributed along its/their cross-section with a contrast in intensity at at least one point inside said cross-section.