1. “Milliarcsecond imaging in the UV- Optical domains: Preparing the way to space borne Fresnel Imagers”, Nice, 23-25 Sept. 2009 INSTALLING A FRESNEL IMAGER ON A 122 YEARS OLD REFRACTOR Jean-Pierre Rivet CNRS, Observatoire de la Cote d’Azur

2. 2 The 76cm refractor Available since:1887 Refurbished in:1966 Focal length: 1789 cm @ 546 nm Diameter:76 cm Mount:German equatorial Dome diameter:24 m Dome weight:  93 000 kg Design:Ch. Garnier, G. Eiffel Registered as an historical monument Still active scientifically...

3. 3 Why on this instrument ? The 76 cm refractor in Nice is: an 18 meters-long optical bench (no beam folding required), on an equatorial mount, easily available, with local scientific and technical environment. 18 m

4. 4 The drawbacks Less than ideal celestial tracking Seeing conditions Light pollution No build-in automatic guiding available Tube flexions Constraints due to the status of historical monument modifications forbidden on genuine parts only fully reversible actions allowed

5. 5 The mechanical layout of prototype “Generation 1.5” Milestones: Prototype Generation 1  laboratory testbed, Toulouse, 2008 Prototype Generation 1.5  first on-sky experiment, Nice, July 2009 Prototype Generation 2  fully featured on-sky testbed, Nice, October 2009 ? Optical rail (field optics, 0 th order mask, correctors, cameras) 18 m refractor tube Fresnel array 76 cm objective lens Not to scale !

6. 6 The optical rail Field optics (Maksutov) Optical rail (2 meters) Imaging doublet 16 mm Blazed Fresnel lens Zero order mask 2-axis fork mount CCD Camera SXVH9 (1) Flip mirror XY motorized linear stages Link to refractor tube Link to refractor tube Not to scale ! Baffles (1) Starlight Express CCD Camera 1392  1040 pixels of 6.45  m. Sensor: Framos ICX285

7. 7 The Fresnel array Laser-machined Copper-Beryllium blade 20cm  20 cm; 700 Fresnel zones (on the ½ diagonal)

8. 8 The Fresnel array

9. 9 Reversible bindings The Fresnel Imager is attached to the refractor tube in a fully reversible way: Refractor tube Steel strip Stay tensioners Shackles Fresnel imager mount Felt soles

10. 10 Fork mount for the optical rail The optical rail’s orientation can be fine-tuned for optimal chromatism correction: Link to the refractor tube Two-axis fork mount Auxiliary refractor (finder) Refractor tube Safety steel strip Optical rail

11. 11 Remote-controlled chromatism correction The optical rail orientation with respect to the Fresnel array can be remote-controlled, to compensate for tube flexions Flexible copper plate Connection pin Motorized linear stages (X, Y) Link to the refractor tube Optical rail Optical rail interface

12. 12 Towards “Generation 2” testbed Full-size blazed Fresnel lens (diameter = 58 mm instead of 16 mm)  available, integrated; to be tested on-sky “Andor Lucas R” science and guiding EMCCD cameras (1004  1002 8  m pixels), with dedicated software  to be delivered soon 100 Hz tip-tilt corrector  lab tested; to be integrated and tested on-sky New generation refractor’s slow motion keypad (computer-driven)  available, integrated; to be tested on-sky Flexion compensators for the optical rail  to be integrated and tested on-sky C1 Expected completion date: November 2009

13. 13 58mm blazed Fresnel lens Diameter:58 mm Number of zones:696 Substrate:Fused silica TO BE TESTED ON SKY

14. 14 100 Hz tip-tilt corrector The imaging doublet is mounted on XY piezo translator, driven by a guiding camera, through a 100 Hz computer-based servo-loop, for real-time correction of turbulent tip-tilt, tube flexion, and celestial tracking defects. Refractor’s slow motion keypad modified to be computer-driven Mechanical support XY piezo translator (replaced by a fake aluminium part on this image) Imaging doublet TO BE TESTED ON SKY C1

15. Thank you for your attention !