The invention is directed to an optical unit for a head-up display comprising an image generator, a mirror and a cover plate which are arranged in a housing one behind the other in the direction of light propagation. The beam path is directed to a windshield. The invention is wherein that the mirror is a rear-surface mirror whose reflection surface has a light-bundling action. The rear-surface mirror has, in addition, a refractive action that can be generated by the refractive index of the mirror material and a material thickness which changes between the reflection surface and the transmissive surface.