Technical Observing - ARGOS Dichroic Tests 20140320 UT

Observers: JHill (Tucson - remote room) MBonaglia, LBusoni and many others on site
Telescope Operator: SAllanson (LBTO)



Test Concept from Marco

Our rough idea for a possible test is the following:
o   Setup the Telescope without dichroic
o    Point at a bright star
o    Collimate the telescope with AGw
o    Reconfigure the telescope with the new config file to compensate the
presence of the ARGOS dichroic
o    Slide in the ARGOS dichroic
o    Check that star position on AGw is unchanged
o    Perform a 360deg rotation of LUCI2 rotator to check for pupil and
field wobble on AGw

John's Expanded TEST with TCS lingo

  • Authorize as LUCI@RFBG (and also @LFBG)
  • Retract the ARGOS Dichroic
  • Preset ACQUIRE to a pointing star and adjust pointing
  • Preset ACTIVE to a star for collimation (could be the same pointing star)
  • Record manually: IE/CA, and the M1 and M2 active optics corrections including the M1 Zernikes

  • Authorize as LUCI@ARGOS
  • Deploy the ARGOS Dichroic (assuming it is not yet automatic).
  • Restore the IE/CA and active optics corrections manually.
  • Preset ACQUIRE to the same pointing star
  • Check that the star position on AGw on-axis is unchanged.


NOTE: This is only a partial log of the activities this night. There were many other ARGOS activities before and Adaptive activities after.

06:00 Collimating at EL=67 deg, agwY=107 mm

DX M1 Z6=-2123 Z9=-211 Z10=40 Z11=-185 Z22=16 Z=-0.015
DX M2 X=0.133 Y=1.734 Z=-0.172 RX=-191 RY=+17

The Dichroic Experiment

07:10 Stop laser propagation, retract dichroic

We are already authorized LUCI@RFBG and IRTC@LFBG.

Without Dichroic at RFBG

07:12 ACQUIRE preset on-axis

Default (raw pointing model) IE/CA -22 -203 (arcsec)

IE/CA are the zeropoints of the pointing model for Elevation and Azimuth (corrected for CosEL).

The centered RFBG (measured here) IE/CA +2 -197 (arcsec)

07:16 ACTIVE preset to gs=1 Y=107 mm

DX M1 Z5=-495 Z6=-2978 Z9=-281 Z10=129 Z11=-115 Z22=-79 Z=-0.059
DX M2 X=0.197 Y=1.740 Z=-0.259 RX=-181 RY=+17

Steve had slightly different numbers written down at a slightly different time so his RX was -190.

With Dichroic at ARGOS

Authorize LUCI@ARGOS

Manually apply the above corrections by adding them into the global offsets. Steve did it while John checked his math.

07:31 ACQUIRE preset on-axis

Default ARGOS (raw pointing model) IE/CA is -22 -203

Now centered star is at IE=-3 CA=-191

07:38 GUIDE preset to gs=1 Why do we miss the off-axis star in the opposite direction? (we miss because of the transform error)

Improve focus by +0.050 mm (the calculated value) moving M2 from -0.243 to -0.193.

07:43 ACTIVE preset to offaxis star gs=1 -- wavefront is fine at Y=107 mm from the axis

07:49 ACTIVE preset now Y=155 mm and 40% of spots are vignetted. Active Optics would not be possible here.

07:52 ACQUIRE preset on-axis

When we moved the dichroic out (but still at ARGOS collimation), the image moved up 2.5 arcsec = 1.6 mm. (The expected amount although John was initially surprised about the direction which was straight up in EL on the parallactic mode preset.)

RFBG without dichroic

08:02 Authorize LUCI@RFBG (dichroic is still out)

08:04 ACQUIRE preset on-axis in parallactic mode

IE/CA -4 -189 which is very close to the ARGOS value (3 arcsec) measured at 07:35. The question is why did the earlier pointing at 07:12 give a different result. Does the tertiary have a bit of hysteresis? (It has not when we've checked this in the distant past.)

Handover for Adaptive

08:10 Handover to JC and JCG for adaptive optics work.


John's telescopework email from February 2014:
        I've added the actual ARGOS focal station M3 selector angles
(angles made larger by 0.07 deg because of the dichroic wedge) to
OSS/positions.conf. Besides getting ready for ARGOS tests, this 0.07
deg will remove all the focal station ambiguity that was causing
trouble with the OSS GUI focal station check.

See Marco Bonaglia's document ARGOS_131007_LBT_recollimation.pdf for

My intention was to also implement the corresponding changes to M1 and M2
at the same time.  This has NOT been done - as I'm running out of day, and
I'm not quite finished with the calculations to convert Marco's angles
into PSF collimation adjustments.

A few days later.......

     I've installed the collimation table changes for M1 and M2 for
the ARGOS dichroics at the ARGOS focal stations.  No changes were
made for LBC, and no changes were made for RETROREF.

In preparation for that, I merged the Global Offsets into the Offset
Collimation Coefficients for both SX and DX secondaries.  That makes
no net change in the collimation models, but all the default Global
Offsets will be 0.000.

Steve: make sure to Refresh Collimation Models, and Reset Inputs for
M1 and M2 so that we don't get stuck in some funny intermediate state.

As far as I am aware, this was the final step needed to make PSF ready
for ARGOS focal station observations next month.


Where we were before for all the Gregorian Focal Stations:
DXSM models were previously DXSMLUCIFERCollimation.20131025.dat
DXPM models remain DXPMLUCIFERCollimation.20111208.dat except ARGOS
SXSM models were previously SXSMLUCIFERCollimation.20131218.dat
SXPM models remain SXPMLUCIFERCollimation.20130123.dat except ARGOS

What updated today:
DXSM models are now DXSMLUCIFERCollimation.20140225.dat
SXSM models are now SXSMLUCIFERCollimation.20140225.dat
With the previous Global Offsets merged into Offset Collimation as
described above.  These were copied to the other Gregorian focal
stations with propagate_DXSMLUCI.csh and propagate_SXSMLUCI.csh.
Note: Many Gregorian focal stations use the same collimation model, and
the old model is saved by date for only one of them (usually LUCI).

The specific M1 and M2 offsets for the ARGOS focal stations
were added as new Global Offsets to:

Where did these new offsets for M1 and M2 come from?

The starting point here is Marco Bonaglia's document

The goal is to translate Marco's results for the M1 and M2 adjustments
into the coordinates that PSF collimation will understand.
The challenge is to get all the signs correct.
Thanks Marco for writing a clear description of your calculation!


From Marco's page 3 we see that we need to point the telescope optics
(M1 and M2 together) 10.8 arcsec toward the horizon.

That repointing is nearly the same as making IE [elevation encoder
zeropoint in the pointing model] more positive.  We don't want to
adjust IE, because that would offload the pointing correction to the
mount when observing in monocular mode.  We want this correction to
stay on the M1 and M2 optics collimation always.

That repointing is also nearly the same as applying +10.8 arcsec of
Optics TIP [PSF definition] as Coma-free Pointing Correction applied
to M1M2 [rotating M1 and M2 as a unit] in PSF. The difference is
that Marco is rotating M1 and M2 about the M3 vertex; while PSF would
normally apply Tip by rotating M1 and M2 about the rotator center in
the F/15 focal plane (to avoid inducing just the motion that Marco is

After consulting the Commissioning Wiki pages for PCS and PSF, the
above paragraphs about IE and TIP are merely to get the correct sign
of the rotation.

The corrections to M1 and M2 positions for elevation correction alone
are as follows: 10.8 arcsec toward horizon (units are mm and arcsec)

M2 dX=0.0 dY=-0.411 dZ=0.0 dRX=+10.8 dRY=0
M1 dX=0.0 dY=+0.117 dZ=0.0 dRX=+10.8 dRY=0


For the azimuth component of repointing, we can use PSF TILT Coma-free
Pointing Correction to get the sign of the optics rotations.

Marco confirms that CW and CCW are as viewed from the sky.

The corrections to M1 and M2 positions for
SX azimuth and elevation correction are as follows: 5.3 arcsec CounterClockwise
(units are mm and arcsec)
M2 dX=+0.216 dY=-0.411 dZ=0.0 dRX=+10.8 dRY=+5.3
M1 dX=-0.058 dY=+0.117 dZ=0.0 dRX=+10.8 dRY=+5.3

DX azimuth and elevation correction as follows: 5.3 arcsec Clockwise
(units are mm and arcsec)
M2 dX=-0.216 dY=-0.411 dZ=0.0 dRX=+10.8 dRY=-5.3
M1 dX=+0.058 dY=+0.117 dZ=0.0 dRX=+10.8 dRY=-5.3

-- %USERSIG{JohnHill - 2014-03-20}%
Topic revision: r3 - 20 Mar 2014, JohnHill
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