AAO Instrument Scientists
UHRF Hardware Notes
This section describes the optical path and components of the
UHRF. This overview is intended for AAT support staff but may be of
interest to visiting astronomers.
1. Coude Projection Factors
2. Light Path Summary
3. The Pre-Slit Room
4. The Coude East Room
5. The Coude East Ancillary Room
The image scale at the coude focus is 1.4 arcsec/mm. The image scale
on the detector is 1.4 arcsec/mm times the projection factor. Projection
factors are as follows:
| Resolution |
Spatial |
Spectral |
| UCLES+TEK |
8.630 |
13.250 |
| UHRF@3E5 |
3.010 |
2.970 |
| UHRF@6E5 |
1.505 |
1.485 |
| UHRF@1E6 |
0.903 |
0.891 |
A summary of the optical light path for the UHRF is as follows:
Coude 5 or calibration lamps - slit assembly/slicer - focal modifier - slit
filters - slit shutter - collimator+echelle -
secondary collimator - cross-dispersion-gratings - camera
lens - focal reducers - camera shutter - CCD detector
To turn on the room lights for the pre-slit room turn the key on outside wall,
located near the entrance hatch.
Calibration lamps and filter slit wheel
The THAR arc lamp is located on the engineered track which replace the
infamous lego track. The UHRF laser (HeNe) is in the black
box on side. This box also contains a quartz lamp. Lift the cover to see
lamps. The UHRF slit wheel is also in this box. The quartz lamp used by UHRF
is mounted on the LF2 filter wheel at position 8.
TV Camera
The TV camera has two positions, on top for UCLES and for UHRF+slit,
at the side for UHRF+image slicer. For UHRF ensure that the Beam Rotator
is OUT (uhrf: BR OUT) or it will hit the TV.
Slit Assembly/Slicer
In most cases UHRF is used with an image slicer which cuts the image
into slicer of width 30 microns. In general use the SLICER for all
frames except flat field (uhrf: SLIT SLICER). The entrance is a
'pin-hole' of size 20 mm (about 1.5 arcsec). The back plate of the
slicer is stopped down with two L-shaped pieces. This is held in place
with three springs - these may need to be clicked back in place. The
drive between SLIT and SLICER positions can be a bit jerky. The slicer
cuts an order into about 35 slices which are masked down to around 24
slices.
For flat fields, use a long and wide SLIT for flat fields to see
pixel-pixel variations. Flats should also be taken through the slicer to see
the geometric properties of the slicer itself.
UHRF can also be used with the slit instead of the slicer although this is
rarely done. The slit mode is only used with the detector at the
3E5 position. A slit width of approximately 0.6 arcsec
then gives a degraded resolution of about 1E5. Note that the THAR lamp
is not on the same axis for the slit and slicer and needs to be
aligned manually for use with the slit. This mode has been used to improve
the throughput on faint objects. However in most cases it is advisable to use
UCLES for objects fainter than around 13th magnitude.
Focal Modifier
The Focal Modifier is always used with UHRF and is set up in the CONFIG
command. The UHRF focal modifier is the short one. There are also two
UCLES modifiers in the pre-slit room, these are longer and thinner.
Filters
Filters are used in UHRF as follows:
For blue wavelengths it is advisable to use a bandpass filter to cut
out scattered red light. Examples are UG11 centred at 3300 and BG12
centred at 4000. Note that this gives some loss in transmission - and
the blue filters have strong red leaks. The two filter wheels are aligned on
the same optical axis - set one to clear position and other to filter position.
For example the command uhrf: SF1 7 will set slit filter wheel 1 to
position 7.
For red wavelengths it works well to use a `cut-on' filter such as
RG630 to cut out scattered blue light and to avoid order
overlap. These have a sharp cut-off profile at the low wavelength edge.
As described in the `UHRF setup procedures', a filter is also used in
front of the TV lens to correct for atmospheric dispersion.
The Schott Coloured Glass catalogue of filters is available in the library.
Slit Shutter
The slit shutter is located in the wall between the
pre-slit room and coude room. It is controlled from CCD commands, or by using
the red panic button in the control room.
Collimator + Echelle
The first collimator slides into place when UHRF is set up and slides
out of the way for UCLES. The lower Hartmann barn door may fall off!
Secondary Collimator
The focus of this is set by a ray trace model of the spectrograph
and is not absolutely correct. Note that UHRF requires SECOLL units to be in
mm.
Cross Dispersers and Camera Lens
U, B, V and R cross-dispersers are available. See tables at back of the
manual for exact bands. There are also two mirrors called MB and MR
which can be used to give the full spectrum.
Focal Reducers and CCD
Two different focal reducing lenses are used to give the 3E5 and 6E5
resolutions. Both lenses move to side for 1E6 resolution. These are
located on a rotating table at the ends of the baffles used with the CCD.
Camera Shutter
The camera shutter is placed in front of the detector and is controlled by
a switch on the panel in the coude ante-room and by microswitches on doors to
the coude room and pre-slit room.
Instrumental Resolution
The detector can be placed at three different positions to give
resolutions of approximately 3E5, 6E5 and 1E6. To change the detector
position, remove the black baffles, check cables are out of the
way, drive CCD to new position and reset the baffles. This procedure is
normally done by the afternoon staff.
Syntel Microcomputer
The Syntel Micro-computer takes commands from the VAX and communicates with
UHRF/UCLES. The Syntel terminal is located in the Coude East ancillary room.
If the Syntel is hung up try Cntrl-C several times. For a list of Syntel
commands see the Coude
spectrographs manual.
Spectrograph Rack and Power Supplies
To power down the spectrograph power supplies and shutter overides for UHRF
and UCLES turn off the switches labelled 5 4 3 2 1 in order and
power then up in the order, 1 2 3 4 5.
Page created: 7th December 1998 by Jessica Chapman
Last Updated by Jessica Chapman on 18th January 1999.
(jmc@aaoepp.aao.gov.au)