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LBT Q4 2007 Engineering
Review
TAL Telescope Alignment.
Highlights and Progress(Q4/2007)
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See INSP for LBC alignment activities
Verified procedure for aligning alignment telescope to Gregorian
rotator axes.
Measured M3 rotator hub to be decentred by ~ 8 mm and tilted by
~ 15’.
Formulated mathematics to calculate asymmetrical aberration for
any combination of decentre and tip/tilt of m2, this is eventually
going into active optics control, using output from AGW to more
accurately determine position of M2. Useful publishable discovery:
when coma is tipped out on-axis, one of the two nodes of binodal
astigmatism is also zero for this field point.
Determined that A-scope is in need of calibration at around the 2’
level.
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Open Issues
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See INSP for LBC related alignment issues.
“Wall-eye” of PMs and other system flexures need to be
quantified and checked against available correction ranges of
optical elements. Some good results so far for LBC, we seem to
be capable of achieving co-pointing with adjustments within
active optics range, need to determine similar data for Gregorian
modes.
AGW and Active Optics. A lot of theoretical work still needed to
optimize the alignment given data from AGW. Adjusting one of
astigmatism, coma, focal plane flatness and pointing while
maintaining the other three requires a lot of detailed analysis.
FPIA shown to be very quirky. Jury still out on efficacy of recent
“improvements”.
Awaiting budget decision on laser trackers, otherwise no large
optics purchases anticipated for Q4-Q1.
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Progress
Q3: LBC Blue alignment can be improved. Possible to check hub
alignment to GR axis using A-Scope.
 Done, 0.5” images achieved with improved alignment
beyond that needing verification.
Q3: “Wall-eye” of PMs and other system flexures need to be quantified
and checked against available correction ranges of optical elements.
Again, the A-Scope set-up for LBC alignment can give some useful
measurements of that.
 LBC results acceptable, more data needed for Gregorian
modes.
Q3: AGW support.
 Ongoing, this becomes part of overall responsibility for
active optics.
Q3: FPIA sensitivity to focus and other low-order aberrations uncertain.
Quantitative investigation underway with Zemax-modelled CCD’s
 Problems identified, possibly solved by implemented
changes, jury still out.
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Progress
Q3: Awaiting budget decision on laser trackers, otherwise no large
optics purchases anticipated for Q4-Q1.
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No Change in 3 months.
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Planning
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Schedule
 Dry run installation of M2 hub in second week of January ‘08.
 Purchase of Laser Tracker in Q1 ‘08 if approved.
 Alignment of rigid secondary in Q1 ‘08.
 Alignment of tertiary mirrors in Q1 ’08.
 FPIA investigation ongoing.
 Continue work on active optics.
Resource
 Assistance from Software, Engineering groups as well as various
Germans, Italians and John Hill.
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