Active optics

The active optics used in telescopes to compensate for the curvature of the mirror, which arises during the pivoting of the telescope.

In astronomy, reflector telescopes are built with ever larger primary mirrors in order to increase the light collection efficiency and resolution can. Above all glass ceramics (such as Zerodur from Schott AG, Mainz, Germany ) are used, since they have a very small coefficient of thermal expansion, are lightweight and allow a very thickness of the mirror. This, however, lose the levels of stability, and when panning, they bend under its own weight, which causes aberrations.

In order to correct these aberrations, the mirrors are mounted on actuators. Be a control unit and compared actual target geometry of the mirror, and the actuators may be a deformation of the mirror, where appropriate be compensated.

The active optics was first used at the New Technology Telescope at ESO, but also the two Keck telescopes, which use four telescopes of the Very Large Telescope ( VLT), the Large Binocular Telescope ( LBT ) and the Gran Telescopio Canarias this technique.

While the active optics compensates for slow mechanical effects of the telescope, adaptive optics reduces the rapidly changing disturbing influences of the atmosphere. The actuators are similar, but operate in adaptive optics iA to a secondary mirror. The sensors are fundamentally different.