A microlithography illumination optical system is used to guide illumination light from a primary light source to an object field. A mirror array of the illumination optical system has a plurality of individual mirrors, which can be tilted independently of one another by actuators and are connected to associated tilting actuators. A controller is used to activate the actuators. A raster module of the illumination optical system has a plurality of raster elements to produce a spatially distributed arrangement of secondary light sources.