TAKING CALIBRATION FRAMES: 
GETTYSBURG COLLEGE 
OBSERVATORY

      
  1. Make sure the dome lights are off (controlled from either the dome or the console with the tube fans and dome fan).
  2. In the PMIS image window, go to user > take bias frames.  Take 10 at the beginning of the evening, and 10 at the end.  Start the numbering at one, and continue the numbering sequence through ALL calibration frames.  Don't restart the numbering for each set.
  3. In the PMIS image window, go to user > take dark frames.  Take 20 dark frames, with an exposure time of 120 seconds each.

    4. *NOTE*  As this step takes some time, it can be left for the end of the evening.  If you do choose to take dark frames at the beginning of the evening, allow enough time before sunset or you will miss your chance for flat fields.
  4. If you are not in the B filter, move to it in the PMIS image window under user > B filter, and, in ACE, move the telescope to the "flatfield" position from the algol.tof database and turn telescope tracking (but not the autoguider) ON, as well as dome tracking.  Once the telescope has moved, select the "flatoff" position in the database, but don't move yet.  This offset will not be used until after taking the first flat field frame.
    *NOTE* If the lower section of the dome shutter is attached to the upper section, move to "flatfield Low" rather than "flatfield".
  5. Just after sunset, in the image window, under acquire > exposure, do a 1000 msec test exposure.  Then in the same window, go to process > measure > imstats to see the Iavg value.  When this value falls to about 20,000 counts, go to user > take flat fields.   Start with an exposure time of 1 sec.  Take 5 frames.  After each frame, a prompt appears, at which time you should move the telescope to the "flatoff" in ACE and then click "ok" on the prompt in PMIS.  After the fifth frame has been taken, when the prompt appears, just click ok without moving the telescope.

    6. *NOTE*  The flat fields must be done quickly once started.  To speed up the process a bit, you can click on the "Go To" button in ACE while the camera is exposing, since ACE will prompt you again before actually moving the telescope.  Leave this prompt up until the camera finishes the exposure.
  6. Change to the V filter under user > V filter, and do another test exposure.   If the Iavg has fallen below 20,000 counts, adjust the exposure time to still get about 20,000 counts in the exposure, and then follow the same procedure as the B filter frames.
  7. Repeat this process for the R filter and then the I filter.  The order in which the flat field frames are taken MUST be B, V, R, I.
  8. Now you're ready to start observing.

 

copyright Laurence A. Marschall, Gettysburg College