CCD Image Calibration - AAVSO

For a more detailed discussion of dark frames see Chapter 7 of Arne Henden’sbook.Flat FramesFigure 4. A typical flat frame. The circular rings are "dust doughnuts" — out offocus images of dust particles on the optical surfaces of your telescope, filters, andcamera.A flat frame compensates for obstructions, reflections, and other problems in thelight path. This is the path light travels from the time it enters the telescope to themoment it strikes the CCD chip. Dust on optical surfaces, reflections from bafflesor poorly aligned optics, vignetting, and other noise sources can interfere withyour final data.Flat fielding is the most difficult calibration routine. There are many things towatch out for and many ways to do it. In fact, some people call it an art because itis so intricate and there are so many creative ways you can do it. The key is to bepatient and realize that your first few flats will likely not turn out well. Take yourtime and with experience you'll be able to master the master flat!The ConceptA flat field is a picture of what's wrong with your system in regards to the path oflight. You will see dust donuts, light gradients, reflections, and more. Now thatyou have an image of what is bad, you take an image of the star. That image is an7