Diapositive 1

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INSTALLING A FRESNEL IMAGER ON A 122 YEARS OLD
REFRACTOR
Jean-Pierre Rivet CNRS, Observatoire de la Cote
dAzur
Milliarcsecond imaging in the UV- Optical
domains Preparing the way to space borne Fresnel
Imagers, Nice, 23-25 Sept. 2009
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The 76cm refractor
Available since 1887 Refurbished in 1966 Focal
length 1789 cm _at_ 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...
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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
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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

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The mechanical layoutof 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, 0th order
mask, correctors, cameras)
Fresnel array
Not to scale !
18 m refractor tube
76 cm objective lens
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The optical rail
Imaging doublet
Zero order mask
CCD Camera SXVH9 (1)
Field optics (Maksutov)
2-axis fork mount
Flip mirror
Optical rail (2 meters)
XY motorized linear stages
Link to refractor tube
Not to scale !
16 mm Blazed Fresnel lens
Link to refractor tube
Baffles
(1) Starlight Express CCD Camera 1392?1040 pixels
of 6.45?m. Sensor Framos ICX285
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The Fresnel array
Laser-machined Copper-Beryllium blade 20cm ? 20
cm 700 Fresnel zones (on the ½ diagonal)
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The Fresnel array
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Reversible bindings

• The Fresnel Imager is attached to the refractor
  tube
• in a fully reversible way

Shackles
Stay tensioners
Steel strip
Refractor tube
Felt soles
Fresnel imager mount
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Fork mount for the optical rail

• The optical rails orientation can be fine-tuned
  for optimal
• chromatism correction

Refractor tube
Auxiliary refractor (finder)
Two-axis fork mount
Link to the refractor tube
Optical rail
Safety steel strip
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Remote-controlled chromatism correction

• The optical rail orientation with respect to the
  Fresnel array
• can be remote-controlled, to compensate for tube
  flexions

Link to the refractor tube
Motorized linear stages (X, Y)
Connection pin
Flexible copper plate
Optical rail interface
Optical rail
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Towards Generation 2 testbed
C1

• 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 refractors 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

Expected completion date November 2009
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58mm blazed Fresnel lens

• Diameter 58 mm
• Number of zones 696
• Substrate Fused silica

TO BE TESTED ON SKY
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100 Hz tip-tilt corrector
C1

• 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.
• Refractors slow motion keypad modified to be
  computer-driven

Imaging doublet
XY piezo translator (replaced by a fake aluminium
part on this image)
TO BE TESTED ON SKY
Mechanical support
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Thank you for your attention !