Fick Observing Manual for Newtonian CCD Imaging
by Guillermo Gonzalez and Joe Eitter
(August 2002)
Background: The Andor CCD is used at the Newtonian focus of the Fick 24-inch
telescope. After passing through some corrective optics, the beam has a focal ratio of
f/4.2 at the CCD. The image scale at the CCD is about one arc second per pixel. A
pellicle reflects about 10% of the light to an SBIG ST5 CCD autoguider camera located at
a right angle relative to the Andor CCD camera. The Andor CCD camera head is sealed
and a high vacuum is maintained within. Multistage thermoelectric cooling allows the
camera to reach an operating temperature of -70ºC in cool seasons, but it requires the use
of the fluid coolant in the summer months to reach the same temperature.
(If you are viewing this manual on a computer, you might consider increasing the
magnification to see additional details on the equipment and computer screen shots.)
Setup instructions:
Steps 1 to 12 can be done before it gets dark enough to observe.
1) Upon arrival turn on the air conditioning/heating as the case may be. In the summer
the control room should be about 78º F; in the winter set it to 68º F. You may want to
open the covers on the windows.
2) Turn on the monitor that displays the video camera aimed at the South wall arrows.
Open the South wall; stop when the arrows match. Then, open the roof. Stop when the
roof and North wall are nearly flush. Do not trust the limit switches for the roof and
wall! Turn off the video monitor when finished opening up.
(Note: This is a good position to leave the slide selector in when not in use.)
3) Go out to the telescope and remove the cover just inside the Newtonian port. Open
the mirror covers. Uncover the two finder scopes if needed. If the black cloth is on the
Newtonian port optics, remove.
4) Turn on the power switch on the power strip by the East side of the pier. Turn on
the coolant fluid pump if necessary. Turn on the Andor CCD power supply on the floor
near the North side of the pier.
5) Plug in the STV all-sky camera power cord and uncover the camera. Turn on the
power to the telescope video camera (by the North wall). Plug in the dome lights using
the "dome lights - flat lamps" power cord.
6) Make certain all the ladders and power cords are positioned to allow for free motion
of the telescope.
7) Back in the observing room, we need to start turning on the equipment that takes the
longest time to reach operating status. In order, these are the Andor, ST5, and STV CCD
coolers. We will do quick starts of these units and return to them later to finish the
setups. First, power up the Andor CCD controller computer. Start the Andor software.
Turn on the camera cooling by clicking on the box on the lower right of the window. Set
the temperature to -70º C.
8) Power up the ST5 autoguider control computer and monitor. Type “ccd” to start the
ST5 controller software. Under the “camera” menu, select “setup”. Set the temperature
to about -25º C below the dome air temperature. Note the cooling current. If it gets above
99% you might have to increase the temperature.
9) On the left side of the control room power up the P5-166 PC on the rack. This runs
the Guide 8.0 star-charting program and controls the STV all-sky camera. Start the STV
software. Set the cooling to the STV using the "setup" and "parameter" buttons. The STV
can be cooled to about -15º C below the dome air temperature. Note the cooling current.
If it gets above 99% you might have to increase the temperature. Start the Guide 8.0
software.
10) Turn on the power to the Newtonian control console above the P5-166 PC monitor.
This unit reads three telescope temperatures (*-1.0ºF), controls the positions of the xyz
(focus-RA-Dec) translator of the ST5 autoguider and the dark slide at the input to the
Newtonian port. Open the dark slide with the toggle switch (hold for about 15 seconds
until the light goes from yellow to green).
11) Now on to the DFM console. Make certain the telescope drive power switches are
off. Turn on the main telescope power. Turn on the DFM computer immediately below
the DFM console. Then, turn on the three switches on the lower left of the console.
Make sure the "object-list - The Sky" switch is in the "object- list" position and the
"East - West" switch should be in the "East" position.
12) Power up the "object lists" computer above the DFM console. Start DOS and then
type ‘sxz’.This will list bright stars near the zenith. One of these stars can be highlighted
and the "s" key will transfer the coordinates to the DFM computer.
Once it gets dark,
13) Turn on the video monitor for the telescope monitoring camera.
14) Turn on the STV all-sky camera display monitor (settings described below).
15) Click “Image” in the STV software to start acquisition. The software will first
acquire a dark frame, and then it will start acquiring images continuously.
16) Close the window blind in the observing room.
17) Check to see if the Andor CCD temperature has reached -70º C.
You are now ready to observe!
Shutting down:
Generally, work backwards from the above procedure. The most important tasks are the
following: 1) turn off the Andor CCD cooling, 2), turn off the ST5 autoguider CCD
cooling, 3) move the telescope to the stowed position, 4) turn off the telescope drives, 5)
cover the all-sky camera and Newtonian port, close the telescope covers, cover finders,
cover STV all-sky camera 6) close roof, 7) close South wall, (make sure the hand levers
for the dome control are NOT left in either the "South Wall" or "Roof" positions) 8) turn
off powered items around the telescope, 9) turn off all computers, DFM console main
power, and monitors. Note, the Andor CCD control software will not let you close it
down until the CCD head has warmed above a certain value. Then, the temperature will
read "Off". The cooling current of the ST5 autoguider should be zero before turning off
the power at the telescope or ending the ST5 program.
Additional observing details:
Summer versus winter observing:
In the summer the roof and walls will move faster than in winter. Do not trust the limit
switches on either the roof or wall! The Andor CCD will require additional air cooled
water when the air temperature is above ~55-60º F. When it is below ~-5º C in winter the
Andor program cannot be ended normally because the CCD temperature will not get
above 0º C. After the cooling current has been off for at least five minutes, you can end
the program by doing "Ctrl-Alt-Del". In summer make sure to turn off the air conditioner
when leaving. In winter set the heat to 62º F. If the outside temperature is going to be
below 20º F or above 80º F place the covers on the windows.
Saving data:
Presently, we save Andor CCD images to 100 Mbyte Zip or CD-R disks. Check the size
of your data folder first to make sure it will fit onto your disk. If you have lots of data to
save on a CD-R disk, start saving when to turn off the CCD cooling. Don't forget to save
a test image in "signed 16 bit fit" format before starting to store images at the start of the
night.
Taking all-sky images with the STV camera:
After the sky is dark, the "Image" and "Parameter" buttons in the STV window can be
used to set the image parameters. Set exposure (= 10 to 30 seconds), gain (= 1x), dark
subtraction (= yes), mode (= continuous), sample time (= 1); the values are set with the
“Value” button. After the image is displayed the "Brightness" and "Contrast" can be
adjusted.
DFM pointing computer operation:
1) Zero the telescope coordinates:
First, Select’ a bright star near the zenith with the object lists computer and press return.
The coordinates should automatically feed into the pointing computer; check that they
appear on the ‘next object’ line. Type either ‘8’ (Go) or hit the ‘Go’ button on the DFM
console. Take an image with the Andor CCD (make sure the Newtonian slide is open; the
V or R filters will give more signal). If the bright star is not in the center of the frame,
then estimate how far you need to move the telescope by calculating the number of
pixels between the star and the center of the frame (one pixel is about one second of arc).
You can use the ‘set offset’ command under the ‘movement’ menu to move the telescope
a small amount. After the star is centered and focused in the CCD frame, you can 'zero'
the telescope coordinates. Type ‘1’ to enter the initialization menu, then ‘2’ (‘set
telescope position”); hit ‘return’ to zero the coordinates. If the star is completely off the
CCD, you will have to use the finder scopes to center the star, then do the above.
2) To move the telescope to a new target, use the “movement menu”. You can use the
Messier object library in the pointing computer with option “3” (“select library object”
[for M5 type 5]), or type in the coordinates with option “1” (“set slew position”), or
feed in coordinates from the object lists computer (using the “ngc” catalog, for example).
3) To take a lamp flat or stow the telescope, go the “miscellaneous menu” and type “5”
(“set flat position”) or "6" ("set stow position"). Note: Don't forget to turn off track on
the DFM console. Go out to the telescope and plug in the flat lamp power. Make sure
the black cloth is wrapped around the Newtonian focus box and the flat target is in the
'normal position' with the South wall in the up position.
The switch for the "dome lamps - flat lamps" is to the lower right on the roof/wall
control console. A second smaller switch on this box, when in the down position reduces
the power to the lamps. Use this switch only when doing the R and I flats. The rest of
the time it should be in the up position.
Using the ST5 autoguider:
1) To setup the autoguider, go the “Track” menu and select “Track” (or type 't', 'r'). The
software first obtains a dark frame, so it instructs you to close the Newtonian slide and
then open it when the dark image has been acquired. This dark frame will automatically
be subtracted from each ST5 image obtained for the remainder of the night, so long as
you do not change the exposure time. Your star should appear in the frame. If not, your
RA and DEC offsets were not correct. Once you have the star in the autoguider field,
adjust the focus with the autoguider focus (not the main telescope focus!) until the image
is round (use the focus chart on the DFM console for the ST5); note, you need to focus
the telescope for the Andor CCD first. To acquire a new image without starting the
autoguiding, hit the “esc” key. Note: the focus for the Andor CCD will be different for
different filters (see below). This will also require the focus of the ST5 to be adjusted for
different filters. As the RA - Dec position of the autoguider is changed, there might need
to be a small adjustment in the focus of the autoguider.
2) If you are confident that the pointing is accurate and you know the RA and DEC
offsets errors between the centers of the autoguider ST5 and the Andor CCD fields, you
can use the autoguider to guide on a 9th or 10th magnitude star in the same CCD field as
your science target. You can use the Guide 8.0 software to find such a star (you can
convert it to a red screen with “Alt-R”). The number “10” field is approximately the size
of the Andor CCD field (18' square). You can get the offset between the center of the
field and the guide star by clicking on the center object with the right mouse button
depressed and dragging to the desired guide star. Then, set the displayed RA and DEC
offsets on the autoguider (and applying the appropriate offset errors, if any).
3) To start the autoguider, go to the “Track” menu and select “Track”. Once the image
comes up, adjust the cursor position to overly the part of the star image with the
maximum counts; note, it might not be the center of the star image. Then, hit the return
key twice. Watch the first few centering residuals to make sure the software does not
lose the star. Once you are satisfied that the guiding is working, you can start your
Andor CCD exposure. If you have guiding problems make sure the balance of the
telescope is correct. Clouds are the most frequent cause of the autoguider to lose its star.
Filters and focusing:
Filters: The filters for the Andor CCD are selected using small while box just to the left
of the Andor control PC monitor.When a switch is in the ‘down’ position, the wheel will
stop at that position. When it is in the ‘up’ position, the wheel will pass by that
position. To save time changing filters, only set those switches in the down position that
correspond to the filters you are using. To start the filter wheel moving, press the red
button for about one second.
Focusing: The focus for the Andor CCD is controlled with the hand paddle just to the
left of the Andor control PC keyboard. The two top buttons control the focus. The
focus encoder value is displayed in red LEDS on the small box just to the right of the
DFM console (one unit of focus change corresponds to 0.0011 inches). Notice that the
focus value is different for each filter. The relative offsets are listed on a small paper just
to the left of the Andor control PC monitor. The focus also varies with hour angle and
telescope temperature. If you want to keep the images centered using a set of filters, you
will need to move the telescope for the different filters. If you change the focus by -32
units move the telescope by 2x-32" = -64" (64 arc seconds to the west). Note also that
the Newtonian focus suffers from astigmatism, resulting in oblong star shapes when not
in optimum focus.
Using Andor software:
There are two ways to acquire images with the Andor CCD control software: 1) with the
green button on the upper left of the screen, or 2) with a program. The first method is
quick and useful when setting up the telescope at the start of a night. The second method
writes more info in the image header. The first time you save an image be sure to set the
type to “16 bit fits signed”. From then on all the saved images will be of the same type.
The images are read out at a rate of 16 _sec per pixel (about 17 sec. for a full unbinned
1024x1024 image). Before saving your first file, make a new folder within the Andor
folder and label it “mm-dd-yy” according to the UT date.
There are three programs that you will find useful: CCDS.pmg (for acquiring
individual science target images), BiasA.pmg (for acquiring two bias images), and
CCDM.pgm (for acquiring multiple images [also dark frames]). You must update the
filename and exposure time before running a program (see example below). These
programs save images without prompting the user. The programs are kept in the
Andor\mm-dd-yy directory. The CCDS program is shown below.
You might also find it useful to use the command line to set the displayed range
of grey levels. For example, “scaledata(#0,500,2000)” would set the lower and upper
values to 500 and 2000 respectively. You can also adjust grey levels with the bar above
the image display box, but it is somewhat tedious. The image display can be magnified or
demagnified with the buttons to the lower left of the image display. To get a better view
of previously acquired images, you can also open the AVIS FITS viewer software,
available on the same PC. When the programs are used a text window is written showing
information about the image taken. This can be stored in the same directory as the data.
The name used is of the form “mm-dd-yy.txt”. Don't forget to store this file after taking
the final image.
Safety issues:
The safe operation of the AndorCCD camera and 24-inch telescope permits others to use
the facility with minimal loss of time for repairs.Some of the operations you perform can
damage the telescope or CCD, so please try to follow these simple safety rules. If you
are tired to the point of exhaustion and can barely keep yourself awake (and are
observing alone), it is better that you close down rather than risk making a big mistake.
At the very least, make sure you leave the telescope in the stowed position, turn off the
drives, and close the roof.
If it is partly cloudy, keep and eye on the all-sky monitor and satellite images on
the internet and check outside periodically to make sure it is not raining. Stow the
telescope and close the roof as soon as you feel any raindrops.
Whenever you move the telescope, watch its motion on the video monitor with
the red lights turned on. If you see that a cable is caught or that the telescope is about to
hit something, then press the red stop button on the DFM console. Don’t forget to turn
off the red lights after the telescope reaches its target. Wind is not usually an issue, given
the shielding offered by the observatory walls, but if the wind is preventing the
autoguider from doing its job, then close down. If the wind is above 30 mph don't open
the dome. It is not a good idea to observe if the air temperature is below -10º F. When
the telescope is on the east side of the pier, do not move the telescope more than 2.00
hours to the east (i.e., the HA should never be more negative than -2).
Characteristics of CCD at Newtonian focus:
-Marconi CCD47-10: 1024x1024 (13_ pixel size).
-Image scale: 1. arc seconds per pixel (f/4.2, 24-inch telescope).
-Field-of-view: 18 arc minutes on a side.
-Readout time at default setting and no binning: 17 seconds (gain = 1.4 e- per ADU);
read time as low as 1 second possible but with higher read noise.
-Maximum filters in filter wheel at one time: 8.
-Net (star – sky) counts in 60 seconds for star with V = 16.07, B-V = 0.53, V-R = 0.32,
and R-I = 0.29 at intermediate airmass with BVRI filters:
B: 3340, V: 9200, R: 11870, I: 6400.
This gives photometry good at the ~1-3% level.