Active Phasing Experiment bench

The Active Phasing Experiment (APE) during integration. The APE has been installed on VLT´s 8.2-metre Unit Telescope Melipal (UT3), from December 2008 to April 2009, with the purpose of gaining experience in controlling segmented primary mirrors in preparation for the Extremely Large Telescope (ELT). The central part of the experiment is the active segmented mirror seen in its red protection on the photo. The ELT 40-metre-class diameter primary mirror will be composed of about 800 hexagonal segments, 1.4 metres wide and 5 cm thick. The ELT will be the largest optical/near-infrared telescope in the world.