A reflective sample, such as a mask, is imaged in an optics system. A radiation source emits a light beam with relatively low coherence. A first focusing element focuses the beam before a mirror reflects the focused beam towards the sample at an incidence angle of between 2 and 25° A pinhole aperture plate upstream of the sample has a first aperture to focus and cut-off the beam diameter to form a more monochromatic beam. The sample is displaced by a mechanism in a direction perpendicular to the normal vector of the sample surface while it reflects the light beam. The reflected beam passes a second aperture in the pinhole aperture plate next to the first aperture on its way to a pixel detector. The second aperture limits the diameter of the reflected beam, thereby adjusting the diameter of the light beam before it reaches the pixel detector.