Transcript Optical alignment and image quality testing at GSFC • Test lead: Bill Eichorn, GSFC Test conductors: George Hartig, Sylvia Baggett, Massimo Stiavelli • Full suite.

Optical alignment and image
quality testing at GSFC
• Test lead: Bill Eichorn, GSFC
Test conductors: George Hartig, Sylvia Baggett, Massimo
Stiavelli
• Full suite of alignment and image quality tests performed
twice: before and after vibe test. 1st epoch : 21 Mar-18 Apr
’03, 2nd epoch ongoing
– WFC3 with non-flight detectors (IR MUX, UVIS surrogate) and
flight POM installed in RIAF with OS (CASTLE) providing OTAlike point source illumination at 633 nm (only)
– During 2nd epoch flat fields in F336W, F439W, and F625W were
also obtained
– Over ~4000 images obtained on both IR and UVIS channels
May 22, 2003
WFC3 Report at the June 03 TIPS
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Optical alignment and image
quality testing at GSFC
• Test objectives:
– Demonstrate Optical Stimulus (CASTLE) performance over field;
develop techniques and procedures
– Obtain pre-vibration (of OA) alignment baseline and compare it
with post-vibration data
– Compare with results obtained at Ball with Mini-Stimulus
– Measure residual surrogate detector alignment offsets for use in
flight detector alignment
– Assess image quality and wavefront performance of the completed
optical assembly
May 22, 2003
WFC3 Report at the June 03 TIPS
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Optical Stimulus (CASTLE)
Rm 150
Bld 29 Clean room
May 22, 2003
WFC3 Report at the June 03 TIPS
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CASTLE Schematic
M4 Ste ering Mirror
Precision Encoders
M3 Steering Mirror
Precision Encoders
• Inverted Cassegrain with
46% Central Obscuration
M1
Stimulus
Relay
Optics
• Images positioned over
field with 2 gimballed
flats - produces pupil
rotation
M2
Switchin g Mirror
Slides in plan e for
Extended Sources
Integrating
Sphere
Target
Plane
Upper Reticle
Point
Sources
WFC3 POM
• Point source XYZ
stage permits accurate
focus adjustment
Fiber Feed
RIAF
OTA Latch Plane
ABC Latches
Lower Reticle
OTA Sta 198.440
Alignment
Monitor
May 22, 2003
Flux Monito rs
WFC3 Report at the June 03 TIPS
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CASTLE/RIAF in SSDIF
May 22, 2003
WFC3 Report at the June 03 TIPS
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CASTLE Test Image Field
Locations
• Measurements made at 16-17 points, uniformly-distributed
over IR and UVIS fields (4-5 used at Ball)
May 22, 2003
WFC3 Report at the June 03 TIPS
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IR MUX Image at Field Center
May 22, 2003
WFC3 Report at the June 03 TIPS
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UVIS Image Near Field Center
May 22, 2003
WFC3 Report at the June 03 TIPS
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UVIS alignment focus scans with
WFC3 corrector and CASTLE
May 22, 2003
WFC3 Report at the June 03 TIPS
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IR channel focus scans feasible
with CASTLE only
May 22, 2003
WFC3 Report at the June 03 TIPS
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Phase Retrieval
• Phase retrieval (PR) analysis measures low-order aberration
content of the system at the detector, including focus
• Sets of monochromatic images obtained at multiple focus
settings, on both sides of best focus, and fit simultaneously
to remove ambiguity
• IDL PR routines developed by Burrows & Krist (ca 1990),
used for COSTAR, STIS, NICMOS, and ACS optical
verification and alignment, and adapted for WFC3
• Only 13 lowest-order terms in Zernike expansion used for
wavefront fit; generally provides good indicator of
alignment state and final optical performance
May 22, 2003
WFC3 Report at the June 03 TIPS
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IR Channel Alignment Phase
Retrieval
Pupil/WFE map
(cold mask)
Measured MUX
image
Modeled (fit)
image
Weighted
difference image
May 22, 2003
WFC3 Report at the June 03 TIPS
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UVIS Channel Alignment Phase
Retrieval
Pupil/WFE map
(OS obsc/spiders)
Measured MUX
image
Modeled (fit)
image
Weighted
difference image
May 22, 2003
WFC3 Report at the June 03 TIPS
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Optical alignment summary
•
•
Phase retrieval and focus scan (CASTLE fiber or WFC3 corrector) techniques
yield similar, repeatable results
Residual detector tip/tilt after alignment at Ball corroborated with CASTLE
measurements using alternative focal surface alignment technique
– Alignment of both detectors should be improved with shim offsets as flight detectors
are aligned in transfer fixture at Ball
•
UVIS detector roll off nominal by 0.8 degrees, position off by ~50 pixels
– Set incorrectly at Ball, will be compensated for flight detectors
•
•
•
IR detector roll nearly perfect (<0.1 degrees from nominal)
IR focus is essentially identical to measurement at Ball
UVIS focus differs by ~0.5 mm (STOPT) from Ball measurement
– Believed to be due to offset in model positions for Mini-stimulus
•
Vibration testing did not alter alignment or image quality apart from a small shift
– identical in both channel – probably due to latches tolerance
May 22, 2003
WFC3 Report at the June 03 TIPS
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UVIS Encircled Energy
Measurements vs. Model
• CASTLE EE measurements require correction for 0.46 central
obscuration ratio (OTA is 0.33), spider width and other
differences from OTA, as well as limited measurement radius,
to predict on-orbit EE performance.
• CEI Spec: EE(.25 arcsec diam.) > 0.75 (goal 0.80) at 633 nm
UVIS,=633
MS (Ball)
OS (GSFC)
OTA
Model: Perfect
=0.015 =0.25
0.67
0.86
0.58
0.85
0.65
0.84
Model: 0.03 RMS
=0.15
=0.25
0.63
0.84
0.55
0.83
0.63
0.82
Actual Measured
=0.15
=0.25
0.62-0.66 0.82-0.85
0.55-0.58 0.80-0.83
?SMOV? ?SMOV?
• EE spec will readily met, goal will likely be achieved onorbit, if flight detector performance and alignment are as
expected.
May 22, 2003
WFC3 Report at the June 03 TIPS
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Flat Field Analysis
C-D amp
May 22, 2003
WFC3 Report at the June 03 TIPS
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Flat Field Analysis
• Many negative pupil images seen in the flat fields. They do
not depend on the filter and have sizes compatible with
what would be espected from dust particles on the surrogate
UVIS detector.
• Vignetting has been found on one corner of the field of
view. It is a triangular area about 400 pixels long and 30
pixels wide at the largest point. Over this area the flux rolls
down by more than a factor 2.
– Not caused by filters, pickoff or channel select mechanism: too
sharp (pickoff) and unaffected by rotating filters/CSM to offnominal positions
– It may be caused either by baffles close to the detector or by the
camera head itself (currently at an incorrect position)
May 22, 2003
WFC3 Report at the June 03 TIPS
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Flat Field Analysis
A-B Amp
May 22, 2003
WFC3 Report at the June 03 TIPS
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Conclusions
• The various sets of measurements are consistent
• The data will allow us to position the flight detectors at the
correct position
• Vibration testing did not significantly alter alignment or
image quality
• Small amount of vignetting in UVIS channel (still to be
investigated)
• EE field center goal on UVIS should be met over the
whole field
May 22, 2003
WFC3 Report at the June 03 TIPS
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