Abstract: A slit projector for generating slit illumination in an eye, including a light source, a slit forming unit and an imaging optical unit along a beam path. The invention facilitates improved freedom to operate in the treatment field. The slit projector includes a mirror arranged between the slit forming unit and the imaging optical unit. A corresponding positioning apparatus facilitates aligning the slit illumination in the eye for a therapy system with a surgical microscope and a slit projector. The positioning apparatus includes a holding element and a fastening element, which can be connected to the surgical microscope and the slit projector, respectively, and a pivoting element including a first connection, by use of which the pivoting element and the holding element are movably connected, and a second connection, by use of which the pivoting element and the fastening element are movably connected.