Mirror Alignment and Performance of the Optical System of the H.E.S.S. Imaging Atmospheric Cherenkov Telescopes

The alignment of the mirror facets of the H.E.S.S. imaging atmospheric Cherenkov telescopes is performed by a fully automated alignment system using stars imaged onto the lid of the PMT camera. The mirror facets are mounted onto supports which are equipp ed with two motor-driven actuators while optical feedback is provided by a CCD camera viewing the lid. The alignment procedure, implying the automatic analysis of CCD images and control of the mirror alignment actuators, has been proven to work reliably. On-axis, 80% of the reflected light is contained in a circle of less than 1mrad diameter, well within specifications.