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[lise] Concept
A hypertelescope is a giant astronomical telescope whose main mirror is composed of many small spaced mirrors arranged very precisely on a virtual spherical or parabolic surface (watch the conference at College de France). This arrangement is called a diluted telescope (Le Coroller et al.).
The light beams reflected by the small mirrors on the ground converge and interfere at a focal point where they form an image. This image is processed in an optical device placed in a gondola.
The feasibility of astronomical observations made with a focal gondola attached to cables some tens of meters above a mirror network was developed at the Observatoire de Haute-Provence:
- construction of a diluted telescope prototype composed of a network of mirrors that follows on the ground the shape of a giant virtual spherical mirror
- development of delicate control and metrology techniques.
Since the image sent to the gondola is faint at the center of the field, the optical device placed in the gondola at Ubaye contains an original optical combination developed at Collège de France. It is called a “pupil densifier”.
Diagram showing the "pupil densifier" ©AL 
Before and after the "pupil densifier" ©AL
Positioned very precisely using 6 cables operated by winches, the suspended gondola that supports the optical device points to the star and follows it through its diurnal movement.
After transformation of the wavefront with the optical device, the image is sent from the gondola to a small ground-based telescope equipped with a camera.
 Photomontage showing the installations of the Ubaye Hypertelescope ©MR
 Diagram showing the motion of the optical gondola on the focal sphere © MR
The image produced by the hypertelescope is an instantaneous direct image, not an image reconstructed after calculations made from successive images.
The optical processing of the light beams reflected by the small mirrors of the diluted mirror produces an image quality similar to that of a monolithic giant mirror – with the difference that in the case of the diluted mirror this image is fainter because the effective total collecting surface is smaller.

The two tripods of the "mirror zone", barely visible in the landscape. View towards the west ©MR,2012