VLT active optics: image corrections

A computer-controlled "Active Optics" system was first developed at ESO in the 1980's. It allows the continuous tuning of the optical system of an astronomical telescope, thus ensuring that it always produces the sharpest possible images of astronomical objects.

The first major telescope to profit from this revolution in telescope techniques was the ESO New Technology Telescope (NTT) at the La Silla observatory. Since it began operation in 1990, 75 adjustable supports below the 3.58-m primary mirror, coupled with advanced image analysis and control software, have made this prototype telescope one of the best in the world.

Each of the four ESO Very Large Telescope (VLT) Unit Telescopes is equipped with the latest, improved active optics system that controls the primary 8.2-m Zerodur mirror as well as the secondary 1.1-m lightweight beryllium mirror at the top of the telescope structure. This system offers complete control of the optical quality, allowing the VLT to take full advantage of the exceptional atmospheric conditions at Paranal. This is amply confirmed by fine quality of the astronomical observations now performed with the first Unit Telescope, ANTU.

In the course of the one-year commissioning period (May 1998 - March 1999), ESO's opticians performed extensive tests and further improvements of the active optics system at ANTU. Here are some interesting examples that illustrate the amazing versatility of this front-line technological system.

The video clip includes all sequences in the series "Wonders of Active Optics" showing the image correcting capabilities with the VLT mirrors.