Device for flat illumination of an object field

The invention is directed to a device for flat illumination of an object field in an optical instrument and to an optical instrument with a device of this kind. Optical instruments of this type are, for example, microscopes, including microlithography simulation microscopes in which a flat illumination, i.e., illumination extending beyond a singular object point, of the object to be examined is required. The device comprises a laser light source and a light-conducting cable with at least one optical fiber through which the light from the laser light source is guided to the object field. The optical fiber is constructed and dimensioned in such a way that the intensity of the illumination light within the cross section of the optical fiber becomes increasingly more uniform along the path from the input-side end to the output-side end, and the illumination light is directed from the output-side end of the optical fiber to the object with substantially homogeneous intensity distribution.