20150311 UT -- Realignment of the Rigid Secondary on SX

Technical Observer: JHill
Telescope Operator: CBechetti
Data Analysis: DLMiller
Other Assistance: MGusick, CBiddick, DAshby, KNewton, JLittle


SX AdSec was removed for scheduled maintenance and the Rigid Secondary was installed in its place. After losing several hours because hexapod was powered off, firmware had not been changed, and hexapod incorrectly cabled, the alignment was completed and confirmed with a small set of field aberration measurements.


Alignment procedure is in BGTechProcedures.

If the Rigid Secondary had been recently on the telescope, the switching of the collimation model files would have been easy. However, several collimation improvements have been made since the end of 2013. Thus, I had to derive a differential correction from the Nov/Dec 2013 collimation models, and apply it to the newer collimation models to get a good prediction of where the Rigid Secondary should be.

I have updated the configuration files (at the start of 20150311 UT):

a) Reverted SX Pointing Models in PCSInstrument.conf from SX_Gregorian.20131218 to SX_Gregorian.20131128. (IE from -52 to -55, CA from -42 to -34)

b) Applied Global Offsets in the SXSM collimation models to where I expect the Rigid M2 to be. Previous collimation model in recent use was SXSMLUCIFERCollimation.20140322.dat (mysteriously dated 20140225 since it was prepared in advance), and the new one is SXSMLUCIFERCollimation.20150310rigid.dat. Superceded by SXSMLUCIFERCollimation.20150311rigid.dat based on the measurements below.

c) Propagated to all the Gregorian focal stations with propagate_SXSMLUCI.csh. The SX Argos positions were not modified.

d) Made the SX "rigid secondary mounted" flag true in psf.conf


Found the SX Hexapod UMAC was still powered off shortly before sunset. Kevin fixed that.

Called Mike G at home to get him to change the SX M2 UMAC firmware to the version with the proper scale factor (SX AdSec hexapod is different than the other two.)

Once on sky we had to spiral to find the 3rd mag star, the star was found very far from the expected location. Expected IE/CA = -55,-34 arcsec. Found star at IE/CA +159,-110 arcsec. The star was very strongly comatic. We found that Tip/Tilt optics motions (Coma-free pointing) moved generally along the correct axis, but with an amplitude 5x larger than expected.

Kevin and John L were able to identify the correct cable connections, but it took ~2 hours to work through all this and correct it.

On-sky Alignment

04:38 Hexapod problem corrected, and on-sky alignment finally begins.

SX M2 needed the following Coma-free pointing to match the previous (rigid M2) pointing model: Tip=-22 Tilt=-18 arcsec . SX M2 also needed +500 nm Z8 and +300 nm Z7 for the eyeball coma correction.

Those adjustments result in the following corrections to the SX M2 collimation:
SX M2 Global Offset X=-0.120 Y=-1.040 Z=-3.750 RX=-368 RY=+240
SX M2 Manual Point X=+0.919 Y=+1.123 Z=0.000 RX=-216 RY=+176.8
SX M2 Active Optics X=-0.466 Y=-0.279 Z=-0.148 RX=+29.1RY=-48.5
SX M2 New Sum GO X=+0.333 Y=-0.196 Z=-3.898 RX=-554.9 RY=+368.3
The New Sums were added to SX Global Offsets for all SX Gregorian focal stations before the start of observing on 20150312 (they were in use manually on 20150311).

Field Aberrations on BS9122 to confirm alignment

Shortly after collimating on BS9122, the active optics was updated to X=-0.722 Y=-0.677 Z=-0.160 RX=70.6, RY=-75.2

04:52 field_collect on BS9122_short

First collimation proceded without convergence, so wfsc images 8-10 are not well focussed.

wfsc image 0029 has a big cosmic-ray-like artifact, and may give the wrong result.

GStar wfsc #
2015311 BS9122_short_field wfsc GCS
0 7
17 8-10
0 11-13
18 14-16
0 17-18
19 19-21
0 22
16 23-25
0 26-27
GStar wfsc #
2015311 BS9122_short_field wfsc GCS
0 28
17 29-31
0 32-33

05:20 Handover to science observations

Data has been moved to /home/lbto/data/20150311_lfbg/


DougM writes:
  The field measurement looks OK for the rigid secondary.
The measurements from Focus, 0 Astig and 45 Astig are
all consistent and show we could move the Tilt/CA by ~ 15\x94.
However, this is close to to the measurement error and would
suggest that this is not worth making a change.

 => Field Data Results
      Motion of the secondary needed to remove bi-nodal astigmatism

              From residual Focus Measurement
                  On-Sky Arcseconds
          Tip =   2.7", Delta IE =  -2.7"
         Tilt =  16.0", Delta CA = -16.0"

 => Field Data Results
             Measured bi-nodal astigmatism

              From 45 Astigmatism Measurement
                  On-Sky Arcseconds
          Tip =   6.2", Delta IE =  -6.2"
         Tilt =  20.8", Delta CA = -20.8"

              From 0 Astigmatism Measurement
                  On-Sky Arcseconds
          Tip =  13.8", Delta IE = -13.8"
         Tilt =  10.7", Delta CA = -10.7"

-- %USERSIG{JohnHill - 2015-03-12}%
Topic revision: r2 - 12 Mar 2015, JohnHill
This site is powered by FoswikiCopyright © by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding Foswiki? Send feedback