2.4. Your first image reductionΒΆ

As your very first experience with reducing (i.e. calibrating) an image you will calibrate one flat frame from the folder float.

Open any one of the flat images whose name begins twi and is in the R filter (these have R in the name).


  1. Double-check the exposure time of the flat you opened. Does it match the exposure time of the master dark you created?
  2. Use the image calculator to subtract your master dark from the flat frame that you opened.
  3. In principle, the pixel values are now all due to light that fell on the CCD. Pick a pixel, and convert the value from ADU to photons using the gain you calculated earlier. How many photons was it?