UT 20130516 Technical Observing - Active Optics Calibration
Observer: DMiller, JHill, OKuhn (Tucson)
Telescope Operator: DHuerta (LBTO)
AO Support: JCGuera (Home)
Telescope Support: KNewton (LBTO)
Instrument Support: (LBTO)
Summary (what I wrote in my note to Issue 4643)
We spent the first hour of the AZ observing on 20130516 doing a jackknife alignment of the SX M2 tip-tilt. Details may be found in the Com20130516 file on the Commissioning wiki.
We took MODS1 images at various secondary tip-tilts covering most of the range of travel.
A simple summary is that we confirmed that the alignment from Sunday night (20130513) is not far off (as we thought on Sunday). We made a small adjustment Tip=-20 Tilt=20 (relative to Sunday) before hand the telescope back to science observing at 04:20 UT.
What we have not explained is why the MODS1 images were so bad on Monday and Tuesday (20130514-15). Our present speculation is that the "bad" images are a combination of:
a) small amount of residual field aberration
b) extreme off-axis guide stars
c) wfs vignetting giving poor collimation at the guide star
d) field aberrations getting confused with MODS aberrations.
See the attached jpg image from tonight showing a star at the top of MODS with various Tip/Tilt settings.
0031 is Tip=-100 Tilt=0
0032 is Tip=-50 Tilt=0
0033 is Tip=0 Tilt=0 (Sunday's setting)
0034 is Tip=0 Tilt=+50
0035 is Tip=0 Tilt=-50
0036 is Tip=-20 Tilt=+20 (where we left it tonight)
The last image is the sieve mask from Monday.
The main conclusion is that 0033 and 0034 are not very different, and the best alignment is probably somewhere in betweeen them.
Advice for observing:
1) pick a guide star as close to the field center as possible
2) avoid stars in the lower right corner where there is wfs vignetting
3) watch out for collimation runaway in poor seeing
Check images with on-axis collimation
02:5x ACTIVE preset on-axis with settings from last few nights (Sunday's alignment)
03:00 Home probe and take 2 sec MODS1 images blue 0025 and red 0028
03:05 SX M2 Tip=-100 Tilt=0
net RX becomes -550 (on the other side of the travel) dIE=+100 arcsec
03:16 Home probe and take 2 sec MODS1 images blue 0026 and red 0029
ACTIVE preset to off-axis guide star x=0 y=-38 mm (too close)
03:26 blue 0027 and red 0030
Jackknife binodal alignment
SX M2 Tip=-100 Tilt=0
(unchanged from above)
ACTIVE preset to off-axis guide star x=0 y=-88 (still in the bottom of the large field)
03:31 blue 0028 and red 0031
SX M2 Tip=-50 Tilt=0
net RX becomes +5 and RY remains ??
03:37 blue 0029 and red 0032
03:42 SX M2 Tip=0 Tilt=0
Sunday's position RX=+486 RY=-70
03:46 blue 0030 and red 0033
03:49 SX M2 Tip=0 Tilt=+50
RX=+501 RY=-559 dCA=-50
03:52 blue 0031 and red 0034
03:54 SX M2 Tip=0 Tilt=-50
03:59 blue 0032 and red 0035
04:02 SX M2 Tip=-20 Tilt=+20
04:05 blue 0033 and red 0036
04:20 Handover to the observers for observing Zheng and Ran while we study the images.
First acq image red 0038 (images look OK in the central part of the field)
They observed for the rest of the night with SX M2 Tip=-20 Tilt=+20
(until 7:35 UT).
SX M2 was cleared back to Tip=0 Tilt=0 (Sunday's settings) for the start of the following night (20130517 UT).
- 16 May 2013