NAOMI is the Adaptive Optics system for the WHT, installed at the GRACE
NAOMI stands for `Natural-guide-star AO for Multi-purpose Instrumentation'.
The Adaptive correction is performed by a 76-element (228 degrees of freedom)
segmented deformable mirror. The distortion of the wavefront, and its tip-tilt
is measured using the Wavefront Sensor (WFS), which consistes of a
sensor (built at RAL, based on an 80x80 EEV CCD39). The most important
lenslet array in the Shack-Hartmann is a 10x10 array, and similarly the
DM segments are laid out on a 10*10 grid with the corners missing.
The tip-tilt motion, also caused by the atmosphere, are removed separately
by a Fast Steering Mirror (FSM), at the rate of several tens of times
per second. Meanwhile, every second, any trend in the tip-tilt motion in
one particular direction is corrected by sending guiding packets to the
In twilight run SloDAR!
Check that the Nasmyth Turret is in the GRACE
position. If not, park at zenith, close the petals and press the GRACE button.
On the TCS::
- USER> STATION GRACE_IRDEROT
- USER> INSTRUMENT NAOMI
- USER> AGSELECT NAOMI
- Zeroset as normal
- USER> CAL LAST
- USER> FOCUS 98.60 (Ingrid, 2011)
A change of focus expands/contracts the Shack-Hartmann spot pattern, which should
fit exactly into the WFS grid. The SA will perform the focus run.
Rotator center and calibrate:
First night after an instrument change only, unless the pointing is bad. Notes say that the rotator centre is not done by the TO (???) since a pickoff mirror inside NAOMI can be accurately positioned at the optical rotation axis of the Nasmyth focus. However in July 2011 the rotator centre was measured by the TO using the acquisition TV (AG3) (see orientation below), and the calibrate done on this position.
Warning: Never slew or even offset when the
AO loop is closed!!
Otherwise you will mess up the Deformable Mirror (DM), which is a bit
delicate! The loop can be opened and closed manually at the TopGui control
or using "loop open/close" command on taurus.
For acquisition move the NCU (Naomi Calibration Unit) to AcqCam-position.
The FOV is approximately 3' in diameter. With PA=0 North is to the left and
East is at the bottom.
The arrows indicate the direction a star moves on uDAS TV when in XY handset
| | PA=0: +--------+
| <--- | | |
| | | |
| | N | |
+------+------+------+ | |
| | | | | |
| | | ---> | ^ | +--------+
| v | | | | E
| | | |
uDAS TV commands and startup:
The camera (AG3) can be used as a conventional science camera as far as uDAS
DAS> run AG3 2 "acq of NGC1162"
DAS> finish AG3
The first command will save the image on /obsdata..., the second forces
- On LEO or CETUS, log in as 'whtobs'.
- Type 'obssys' or 'obssys dev' in the pink window and select option 'manual
- Type 'startobssys' in the pink window.
- To start the camera running as a TV then type 'startudasag AG3' in
pink window, followed by option '9'.
- Windows and binning can be set up using the usual uDAS syntax. This is
useful as it speeds up read-out and therefore acquisition,
e.g. window AG3 1 "[400:780,200:600]".
- The reference position for acquiring on the WFS is x=
575 and y= 476 (01/07/2005) (no window, no
Move the star to the reference position on the TV.
Once the object is acquired the NCU is moved to Science-position.
Now the star should appear in the Wavefront Sensor. You might need to tweak the position according to the instructions of
the person in charge of NAOMI.
There is a new tool called Adquisition Tool running on Taurus,
this new tool allows the astronomer to center the objects in the center of OASIS
or INGRID. This Tool uses the acquisition camera AG3.
IMPORTANT: When the Acquisition tool is going to be used is it necesary
to stop the whatever acquisition from the computer that is running AG3. PC close
to the Taurus monitors
The arrows indicate the direction a star moves on the WFS when in XY handset
| ^ |
| | |
| | | |
| --> | | | <-- |
| | v | |
| | | |
Note that switch-box for autoguider has to be set to
The NAOMI Autoguider is sourced from an RS232 line from the Navis computer
in the control room. Images are piped directly to the display tool. Guiding packets come from the AO loop, specifically from drift found
in the Fast Steering Mirror (FSM), which takes out pupil motion (also called
Tip-Tilt). Since there is no guiding when the AO loop is open, you don't
need to turn AUTOGUIDE OFF, even when re-acquiring (unless AO loop has
The guide star can be the target itself ("self-referencing"), if the
latter is sufficiently bright and sufficiently pointlike (< 1.5 arcsec,
say, to be smaller than the sub-aperture guide boxes on the wavefront sensor).
The guide star cannot be brighter than V = 4, or K ~ 5, because of saturation
of the wavefront sensor or science detector respectively. There should
be no stars of similar magnitude within ~ 5 arcsec of the guide star, to
avoid confusing the wavefront sensor.
Observing with the AO guide star off-axis:
- Closing guiding loop:
USER> AUTOGUIDE ON 50 50
The numbers are "pseudopixels", 50 is the center position of the Fast
- Closing AO loop:
The AO loop is closed using either either button on TopGui or
The WFS assembly includes a "pick-off" mirror (a probe) that allows the
AO guide star to be followed by the WFS off-axis, while the science target
is on axis.
- You start with the pick-off on axis and star light on the WFS.
- Move the telescope to put the science target on axis.
- Move X and Y positions of the pick-off to compensate for the telescope
offset and to pick up the star light again. Moving the telescope North
requires a +y movement of the pick-off, moving East a +x movement.
- It is a good idea to do these movements step-by-step.
NAOMI Observing "modes":
NAOMI has 3 different Shack-Hartmann lenslet arrays, the choice depending
on the seeing. The "good seeing array" and "poor seeing array" both have
10x10 lenslets, but the latter have much shorter focal length, so that
they produce less spot movement. This should be used iif natural seeing
is > 1.2 arsec approx. There is also a 4x4 lenslet array for "even worse"
Additionally, the WFS can be read out with 3 different binning arrangements:
"full frame" (6x6), 4x4 and "quad-cell" (2x2), these numbers referring
to the pixels assigned to each Hartmann spot. Increased binning allows
you to increase signal-to-noise on fainter stars AND to read out faster
(which should help with poorer seeing, but in NAOMI, has not yet been proved
to do so...).
Each combination of lenslet array and binning is referred to (by NAOMI
designers) as a "mode".
The most important ones are modes 1 and 2, while mode 8 was also tested
(didn't work). Mode 1 corrresponds to ["good seeing" lenslets + full frame
readout] and mode 2 is ["poor seeing" lenslets + full frame readout"].
Mode 8 is [4x4 lenslets + quad cell readout].
NAOMI Optical Optimisation:
The shape of the Deformable Mirror (DM) and the response of the Wavefront
Sensor (WFS) are optimised using this procedure (see Frank Gribbin's
for more detail):
- Remove relative tilt between the segments of the DM, using "Fisba"
laser interferometer. The result is that the segments should be parallel,
but may have step ("piston") differences.
- Run "Simplex" (also called "Nathanisation") using the White-light interferometer,
to remove "step" error between DM segments. This program allows quick read
("grab" mode) of INGRID, so that you can see the image becoming a sharp
- Run procedures to remove remaining "staircase" errors, so that the image
on INGRID consists of a single point ("staircase" causes multiple images).
- Now that the DM is "tuned" to be flat and ALSO compensates for static optical
aberrations in the INGRID optics, we can proceed to measure WFS "offsets"
(distance of spots from "nominal" centers, which is where they would be
if there were no optical aberrations...). This is done using a pinhole
light source. The "offsets" are different for each Shack-Hartmann lenslet
array and each binning "mode" of the WFS readout. Once measured, they give
the WFS its "starting points" and allow it to send corrections appropriate
to the optical setup in use.
- Test the whole setup using the "wavefront reconstructor" algorithm. This
makes sure the response of the DM to tilt is to remain parallel. The result
should be a stable image on INGRID when the FSM is moved a small distance.
Now ready to be adaptive!
Observing Support Assistants
Last modified: 14 July 2011