An illumination apparatus for an optical system is disclosed, the illumination apparatus (1) encompassing a single light source (2) that emits broad-band light into an illumination beam path (2a). Placed after the light source (2) in accordance with the present invention is a filter system (4), with which several wavelengths or wavelength regions are separable and are guided through a light-guiding means (22) to an optical system (5). The filter system possesses several reflecting filters (8a, 8b, 8c, 8d) which are arranged in such a way that a selected wavelength is guidable by way of those reflection filters and leaves the filter system (4) parallel to the illumination beam path (2a).