6. CCD Acquisition

The program ``CCDTool'' is a windowing application written by John Denune of San Diego State University to control the San Diego State CCD controller. We are in the process of modifying it for use at the Burrell Schmidt.

6.1 A Typical Run
Starting up

  • The grey power box on the side of the telescope needs to be turned on for the CCD and filter wheel to work. If you are standing by the dewar, facing the telescope, then the grey power box is above the dewar.
  • Log into ``budgie'' as observer. Use the password which is given on the monitor. In an xterm window, type:
    ccdtool &
    to start the ccdtool program. A window titled CCDTool should appear (see Figure 6.1 ). There are buttons on this window for Setup, Expose, FITS, DSP, and Quit.
  • At the start of the night or the start of the run, open the setup window. Using the File button at the top of the setup window, load obs.setup. Once the obs.setup file has been loaded, hit the ``apply'' button at the bottom of the Setup window. The Setup window should look like Figure 6.2.
    Important Note: After loading the setup file and before observing, uncheck the ``Reset Controller'' button. Resetting the controller causes garbage to be sent. Two or three ``Flush CCD'' commands (see the Exposure Window, Figure 6.3) should clear things up.

    The CCD controller needs two files which configure boards within the controller. Check in the Set-Up window that the ``Timing Board'' file is /data1/home/cwruobs/camera/obs.lod and that the ``Utility Board'' file is /data1/home/cwruobs/camera/util.lod. (The leading /data1/home/cw may scroll off the front; backing up with the left arrow key should allow you to see the whole path name.) Deinterlacing should be set to serial.


    Taking an Exposure

  • Move the filter wheel to the desired filter, using kermit and schcom (see Sect. 3).
  • Update the FITS header. The button on the CCDTool window (Figure 6.1) labelled ``FITS'' lists the information that CCDTool writes to the image header and gives the observer an opportunity to update some of it.   Figure 6.4 is an example of the FITS header editor window.
    WARNING : At this writing (11/9/98), not the information the user may want is being written to the headers. The filter, the locations of the overscan and data sections (which are needed for the IRAF tasks ccdproc and quadproc ), and a title are not included in the header. We are in the process of adding these to the headers but urge users to check the FITS editor window as well as their images to see what's being written to the headers.
  • Check: Is the ``Reset Controller'' button on the Set-Up window (Figure Figure 6.1) unchecked?
  • Start the Expose window from the CCDTool window (see Figure 6.3).
         * Set the exposure time in seconds. Exposures as short as 1s are ``ok''.
         * Set the number of exposures.
         * Give an image name and extension (.fits). Both budgie and dingo are running IRAF v2.11, which allows the user to work directly with the FITS images, without having to ``rfits'' them first. To work directly with the FITS images, IRAF requires that the images' names end with the extension .fits.
         * By default, the images are written into the directory from which CCDTool was started. If you want to change this, you can give a different pathname with the image name and extension.
         * If you want to use autoincrement, give the first image a name like n1001.fits and CCDTool will name subsequent images n1002.fits, n1003.fits, etc.
  • Press the ``Expose'' button. The ``Expose'' button will disappear after you press it and will be replaced with ``Abort Exposure'' and ``Pause Exposure'' buttons.

    If the exposure is longer than 5s, a countdown will appear at the bottom of the Expose window.

    When the exposure is finished, ``Reading Out CCD...'' messages will appear in the CCDTool and Expose windows. At the end of the readout, a message saying ``Exposure Sequence Completed'' will appear in the CCDTool window.

    The DISPLAY option doesn't seem to work.

    Note: Sometimes the fiber optic link between budgie and the CCD controller doesn't come up correctly when you start CCDTool. If there are no counts in your image, press the restart button on the grey power box (above the dewar on the side of the telescope).

    Twilight Flats

    We find that the best place to take evening twilights is about 100 degrees away from the setting sun, ie 10 degrees over to the east from the zenith. This is where the sky brightness variations are minimized. We leave the tracking on and move the telescope between successive flats.

    Focus Exposures

    You set the telescope focus by hand. The focus readout is an LED just to the right of budgie's console in the dome. The focus varies with temperature and (less) with position on the sky. We recommend taking a focus exposure at the position of each new field to make sure, unless you have moved less than 10-20 degrees in the sky since the last one.

    You currently need to do focus exposures manually, using the buttons on the right hand side of the Exposure Control window (Figure 6.3).

  • Flush the CCD
  • Open Shutter, count desired exposure time, close shutter
  • Shift N lines
  • change to next focus value and repeat the open/close/shift sequence
  • repeat for as many focus values as required
  • readout CCD, save to disk
  • at end of exposure sequence, hit apply on setup window to get idle going again.
  • note that when you take an exposure this way, the disk filename does not auto-increment.

    Note: CCDTool requires most of budgie's memory in order to run well. You should only run CCDTool and schcom on budgie, using dingo for other applications. If you run other processes on budgie, pieces of your images may be dropped by CCDTool. Running on dingo, and redirecting display to budgie will probably not affect CCDTool.

    Quick look exposures: There is a file called acq.setup, which loads acq.lod, with a faster readout time, for acquiring fields. Remember to switch back to obs.setup for science exposures.

    5. The CCD System    7. Troubleshooting