Roberto Ragazzoni
INAF – Astronomical Observatory of Padova
roberto.ragazzoni@inaf.it
Feasibility of the aspheric lens
Catania, June 11 2014
On behalf and with extensive inputs from the Telescope Group (D. Magrin, D.
Piazza, W. Benz, J. Farinato, S. Basso, M. Ghigo, M. Munari, P. Spano’, G. Piotto,
M. Barbieri, E. Pace, S. Scuderi, I. Pagano, L. Gambicorti, C. Arcidiacono, R.U.
Claudi, V. Viotto, M. Dima, G. Gentile, R. Canestrari, S. Desidera, S. Benatti)
Roberto Ragazzoni
INAF – Astronomical Observatory of Padova
roberto.ragazzoni@inaf.it
Feasibility of the aspheric lens
Catania, June 11 2014
On behalf and with extensive inputs from the Telescope Group (D. Magrin, D.
Piazza, W. Benz, J. Farinato, S. Basso, M. Ghigo, M. Munari, P. Spano’, G. Piotto,
M. Barbieri, E. Pace, S. Scuderi, I. Pagano, L. Gambicorti, C. Arcidiacono, R.U.
Claudi, V. Viotto, M. Dima, G. Gentile, R. Canestrari, S. Desidera, S. Benatti)
The aspheric issue…
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We have been asphericized by an hard life (thank you
Silvio…)
We had two offers from manufacturer for actually making
one (in S-FPL51) for test (SESO & Silo)
We have a detailed plan and feasibility by Sagem-Reosc that
already manufactured two similar sets for a different space
project (and they made similar comments as Zeiss quotation
in RUAG report!)
ESA challenged themselves to improve Thales design to
achieve performances and found they need two aspherics
Asphere is on a lens with one flat surface
MediaLario is testing their manufacturing abilities on glass
S-FPL51
The aspheric issue…






We have been asphericized by an hard life (thank you
Silvio…)
We had two offers from manufacturer for actually making
one (in S-FPL51) for test (SESO & Silo)
We have a detailed plan and feasibility by Sagem-Reosc that
already manufactured two similar sets for a different space
project (and they made similar comments as Zeiss quotation
in RUAG report!)
ESA challenged themselves to improve Thales design to
achieve performances and found they need two aspherics
Asphere is on a lens with one flat surface
MediaLario is testing their manufacturing abilities on glass
S-FPL51
The team background
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Rosetta Wide Angle Camera design
 An off-axis tilted FoV design with aspheric mirrors
 Emphasys was on detection of faint gasesous
features from comet nuclei
 Clean PSF: unobstructed pupil, monochromatic
and low scatter design
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None of the above does apply to PLATO!
Several ground based 4m and 8m class
instruments (all with aspheric surfaces)
Postcards sent around…
Postcards sent around…
January 2010
Isabel Escudero
Purpose of study.
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Modify Thales design as follows:
Entrance aperture diameter: 15% bigger.
FOV: from a circle of 28º diameter to a square of
28º side length.
Image: quality equivalent to that of Thales design
for the whole new FOV (criterion is 90% EEC
diameter)
Focal length: same as original
Add Fused Silica plate in front
Aspherics necessary?
Comparing sizes.
Thales
Science
10:11:01
10:01:23
50 .0 0
plato_thales
15:48:36
ME
50 .0 0
plato_v10
Plato_v10
ME
5 0 .0 0
MM
11 -J an - 10
Science
MM
08 -J an - 10
5 0 .0 0
plato_v20
Plato_v20
MM
1 5 -J an - 10
15:49:3 7
ME
MM
08 - Ja n -1 0
Comparing performance
System
Thales
Science
Plato_v10/Plato_v20
EPD (mm)
83
120
95.45
Design
Field object (degrees)
Plato_Thales Axis/9.6/13.7º/19.6º
Axis/9.6/13.7º/19.6º
Plato_v10
Axis/9.6/13.7º/19.6º
Plato_v20
Design
Plato_Thales
Plato_v10
Plato_v20
Science
Field Object
14º
19.6º
19.6º
14º
EFL(mm)
239.5
247.5
239.5
FOV
28º diameter circle
28º diameter circle
28º side square
Diameter of 90% encircled energy (µm)
34.8 / 42.6 / 58.9 / NA
39.7 / 34.4 / 41.8 / 65.8
31.9 / 34.0 / 42.8 / 59.6
Incidence Angle at image
26.7º
38.3º
38º
31º
Distortion (%)
0.7
0.7
2.0
2.9
Conclusions: Thales_v10/_v20.
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Two aspheric surfaces are required for larger EP &
FOV.
If FOV = 28º diameter circle, one aspheric surface is
enough.
Fused silica plate becomes a lens: curvatures and
aspheric are needed.
Note values of distortion (=> calibration and postprocessing for field superposition).
Note large angles of edge field object at image
plane: relevant for radiometry.
Conclusion by ESA…
Do we need aspheres…?
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Yes…
Accordingly to ESA (upgrading of THALES design) at least
two;
With our own design (actually all the “last” versions) just
one.
Feasibility strategy
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ESA never questioned feasibility of one TOU
ESA often being concern about “mass” (well,
sort of…) production
Construction is one of the issues..
We focus on demonstrating a fast procedure
(less than one week) in the warm…
Aggressive plan to demonstrate we can
handle CaF optical elements
TOU BreadBoard
Back Reflected Light
B/S Iris2
CCD
Frame connected to the
bench, allowing the rotation
for lenses insertion from the
top and their alignment
similarly to what would
happen with the final
structure, with
the possibility to be
rotated of 180º to insert
the lenses from both sides
(L3 will be the first one)
TOU Dummy Structure
Iris1
Rotating points
Beam Expander
Transmitted Light
Laser
CCD
Alternative designs
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A design with an aspheric CaF (because SESO
claimed that with some manufacturing
process that would be easier/cheaper/faster)
A design CaF-free (in case we fail space
qualification of CaF lens)
A design taking into account the common
directives of manufacturer
Design 4
BK7 G18
BK7
CaF2
N-KZFS11
CaF2
S-FPL53 KZFSN5
Design 4 - EE
2×2 pixels2
90%EE<30×30 arcsec2 ~ 2×2 pixels2
90%EE<37.5×37.5 arcsec2 ~ 2.5×2.5 pixels2
90%EE<45×45 arcsec2 ~ 3×3 pixels2
Design 5
BK7 G18
S-FPL51
S-FPL53 KZFSN5
N-KZFS11 S-FPL51
BK7
Design 5 - EE
2×2 pixels2
90%EE<30×30 arcsec2 ~ 2×2 pixels2
90%EE<37.5×37.5 arcsec2 ~ 2.5×2.5 pixels2
90%EE<45×45 arcsec2 ~ 3×3 pixels2
Baseline - EE
90%EE<30×30 arcsec2 ~ 2×2 pixels2
90%EE<37.5×37.5 arcsec2 ~ 2.5×2.5 pixels2
90%EE<45×45 arcsec2 ~ 3×3 pixels2
The CaF issue…
Already flown…
One company (SESO) would prefer as asphere
Baseline design has CaF in the spherical, smallest
and more protected position (L3)
 We have in our hand a produced L3 identical to the
flight one (assuming baseline)
 We have two blanks similar in size, glued to the
same holder and cured in two different ways now in
CNES and UniBern for thermal and vibration tests…
 We have an acceptable, although not brilliant, B
plan CaF-less
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Foreseen Activities (CaF2):
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Shipped blank to PD 
Shipped to SG
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Gluing blank
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Curing (th.cycle)
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Shipped to PD
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Shipped to UniBE
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Vibrating
Shipped to CNES Survived!
Thermal cycling
Shipped blank to PD
Shipped to SG
Gluing blank
Shipped to PD
Shipped to CNES
Thermal cycling
Survived!
Foreseen Activities (BB):
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Mounting lenses on mounts (gluing)
Aligning within tolerances
Testing the “warm” optical quality
interferometrically
Measuring the “warm” PSF directly
Measuring the “warm” PSF via Hartmann
Measuring the “cold” PSF directly
Measuring the “cold” PSF via Hartmann
Validation or lessons learned of the alignment
process
One aspheric done on purpose…
Various studies issued…
Various studies issued…
Production plans…
Production plans…
Production plans…
Summary…
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Selex: Ok with industrial plan
Sagem/Reosc: Ok with industrial plan
MediaLario: Interested, feasibility Ok, now joining Selex?
Seso: Ok but would prefer CaF2 (technology driven)
RUAG: Market analysis…
 Zeiss: doable, delivery time non critical
 Asphericon: doable at the limit (delivery time) of their abilities
 Steinbeis TransferZentrum: identified several technologies
 Leica: doable, but reccomending harder material
 Fisba: they do not have capabilities (in spite of…)
 PrazisionOptik: they do not make aspheres
 SwissOptics: they think are doable but exceed the size they handle
What is next…?
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Regain informal contact with all industries
(some already made on their own… Sagem & MediaLario)
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Select one or two for an updated formal
adjourned contact
Place the accent on the serial and industrial
production
Take –very fastly- a final choice as the overall
baseline based on existing informations