a radiation source la a first object table mask table mt provided with a mask holder for holding a mask ma e g a reticle and connected to a first positioning device pm for accurately positioning the mask with respect to item pl a second object table substrate table wt provided with a substrate holder for holding a substrate w e g a resist coated silicon wafer and connected to a second positioning device pw for accurately positioning the substrate with respect to item pl and a projection system u201c lens u201d pl e g a mirror group for imaging an irradiated portion of the mask ma onto a target portion c e g including one or more dies of the substrate w as here depicted the apparatus is of a reflective type i e has a reflective mask however in general it may also be of a transmissive type for example with a transmissive mask alternatively the apparatus may employ another kind of patterning device such as a programmable mirror array of a type as referred to above the source la e g a hg lamp an excimer laser an undulator or wiggler provided around the path of an electron beam in a storage ring or synchrotron a laser produced plasma source or otherwise produces a beam of radiation this beam is fed into an illumination system illuminator il either directly or after having traversed a conditioning device such as a beam expander ex for example the illuminator il may include an adjusting device am for setting the outer and or inner radial extent commonly referred to as u03c3 outer.