An optical imaging system, for example, for a surgical microscope (100) has a beam deflecting unit in order to cast light rays out of an object region (112) into an image plane (104) with an optical beam path. An optical phase plate (107) is mounted in the optical beam path. In the optical imaging system, a unit for generating a geometric image of the image plane is provided, for example, an ocular unit (105). The optical phase plate (107) is arranged on the end of the objective lens (101) facing away from the object or is arranged in a region of the optical imaging system in which the beam path is parallel.