Illumination system with reduced energy loading

An illumination system having a rod integrator and an objective for imaging an object field onto an image field, which has an entry surface, an exit surface, and reflecting side surfaces. A lens-free interspace with an axial size of at least 30 mm is in the objective. A plane within this interspace is optically conjugate to the plane of the entry surface. All rays starting from a central field within the entry surface that are not reflected at the side surfaces have smaller ray heights in the lens-free interspace in relation to the optical axis than all the rays starting from the central field that are reflected at the side surfaces; the ratio of the field width to the width of the entry surface is at most 0.7. The ratio of the field height to the height of the entry surface is at most 0.7.