Defocussed photometry: checklist

1. Select the correct filter (usually R or I).
    
2. Acquire the target. Save the (focussed) image.
    
3. Position target and comparison stars on nice parts of the CCD.
    
4. Binning: do not bin.
    
5. Windowing: window down to the area indicated in the finder chart.
   Record the windowing parameters.
    
6. Defocus the telescope so the maximum counts per pixel from the TARGET star are between 250,000 and 350,000.
   Record the focus value.
    
7. Start the sequence of images using the multiexposure option in the GUI.
   The default exposure time is 100s but shorter exposure times are sometimes used.
   Longer exposure times should never be used.
    
8. Start the autoguider.
    
9. Check the shutter-opening time of one exposure and note the details in the night log.
    
10. Relax. Monitor the observations to ensure the counts per pixel for the target star don't go above 350,000.
    If they go above 350,000, then decrease the exposure times appropriately.
    DO NOT change focus setting.
     
11. Stop the observing sequence at the time specified (generally one hour after the transit has ended).
    Refocus the telescope and take one more image of the field.
     
12. Flat fields: the more twilight flats the better. Use the correct filter and no windowing.
     
13. Send a night report to John S, Uffe and Martin D. Include:
    • the observers
    • when the transit observations started and ended
    • focus and guide star parameters
    • CCD window parameters
    • any problems
    • fits files names and where they can be obtained from
    • the timing check of one observation