An apparatus for inspecting a photomask, comprising an illumination source for generating a light which illuminates a target substrate, objective optics for receiving and projecting the light which is reflected from the target substrate, the objective optics includes a first mirror arranged to receive and reflect the light which is reflected from the target substrate, a second mirror which is arranged to receive and reflect the light which is reflected by the first mirror, a third mirror which is arranged to receive and reflect the light which is reflected by the second mirror, and a segmented mirror which is arranged to receive and reflect the light which is reflected by the third mirror. The segmented mirror includes at least two mirror segments. The apparatus further includes at least one sensor for detecting the light which is projected by the objective optics.