Figure 1 : Elliptical array of telescopes . A giant paraboloïdal dish P,
having its focus in C, intersects the ground plane G along an ellipse.E.
Telescopes located on the ellipse have their optical axes parallel to the
paraboloïd's and feed coudé beams towards a common focus in C.
Optical path lengths are equal. To track a star, the paraboloid may rotate
around C, and coherence can be maintained by moving the telescopes to follow
the deformation of the ellipse. Alternately, additional moving mirrors can be
inserted in the coudé trains . The IGT project involves 27 telescopes
of 8 to 10 meters, mobile on a flat site spanning several kilometers.