Intensity scan of a small pinhole (1.4 µm in diameter) through the focal plane of the KB system. The detector was a photodiode. Prominent side lobes are visible in both the horizontal and vertical directions. Note that the slits S1V, S1H and S2H were all set to a width of 100 µm during the scans, i.e. the incoming beam was considerably confined before entering the KB system.