On Paranal ESO operates the ESO Very Large Telescope (VLT) with four 8.2-m Unit Telescopes (UTs). Each UT can work independently, in which case it sends the light beam towards either a Cassegrain or one of two Nasmyth focus stations for facility instruments.б In addition, the UTs can work together to form an interferometric array (VLTI): in this case, they send the light beams towards their Coudц© focus station, where adaptive optic systems correct the light beams for atmospheric turbulence before forwarding them to an interferometric laboratory to be coherently combined.
ESO also operates four 1.8m Auxiliary Telescopes (ATs) which form the VLT interferometer small array (VISA).
Currently, 12 instruments are operational and offered for science observations. Furthermore, ESO also operates two survey telescopes, each with its own instrument: the 4-m infrared VISTA, and the 2.5-m visible VST.
During the current, P96 period (April to September 2015) the VLTI is out of operation while the interferometric laboratory is being refurbished before the arrival of new instruments.