Dome Flat Optimal Exposure Measurements

Data Taking:

• 1. The rule of thumb is to aim for dome flat levels of about 1/3rd of full well. For the PreCam CCDs, full well is between ~110,000 and ~140,000 electrons. Thus, the optimal dome flats will have background levels of ~40,000 - 45,000 electrons above the bias level. At the gain used by the PreCam CCDs, this is about 8,000-10,000 ADU above the bias level. (Don't obsess, though: we are just aiming for roughly 1/3rd of full well.)

  2. Due to shutter timing issues, one should not drop below about 15 sec for a dome flat exposure.

  3. With all the LEDs on except for the 810nm, the range of exposure times for 10,000 ADU is 5-15 seconds, too short.

  4. Aiming at 20,000-30,000 ADU gives exposure times of 15-30 seconds for g,r,i,z,y.

  5. If exposure times are significantly longer than 60 sec, Darren can provide instructions on how to make the lamps brighter (this is not trivial, though).

Data Analysis:

• 1. Note down the lamp voltages and exposure times for each filter in that night's Night Log.

  2. lamp voltages? where are those?