This is the first time that I'm really inspecting the calibration images we were taught to take/use during data reduction, and I've noticed something in all the flat fields.

The image below clearly shows a grid of darker pixels with 728x36 cell dimensions. Flat Field with dark grid artifact

The camera used was the SBIG STL-6303 according to the FIT headers, which uses a Kodak KAF-6303E CCD according to the online data sheet.

The CCD dimensions, these cell dimensions, and all the binning options are all perfectly divisible, so I'm assuming this artifact is due to the structure of the CCD.

I plotted the mean pixel value of each row to make sure this wasn't an artifact from the image viewing software. The plot clearly shows a drop every 36 pixels.

So, I'm hoping for some confirmation: Is this decreased sensitivity due to the structure of the CCD?

If so, what about the CCD structure actually causes this?

Edit: I should add that a bias frame has already been subtracted from this flat field.

  • I would love for any astro photographers here to recommend online forums, Q&A sites, or any other community-type sites for astro photography, especially with a focus on data analysis and/or astrophysics. I have so many unanswered questions regarding the errors introduced during calibration. Thanks! – astro101 Aug 4 '14 at 0:40
  • It can't quite see the pattern you mention on my screen. However, from working in a lab many years ago, I know you also have to look at the signal processing after the photodiodes. At least to disqualify it as the source of the pattern. – B Shaw Aug 4 '14 at 3:05
  • This question might get more answers at astronomy.stackexchange.com ? Also for other resources you could check out the forums section at astronomynow.com/resources.shtml – James Snell Aug 4 '14 at 7:41
  • Thanks B, James. I'll see what the astronomy.stackexchange.com guys say. – astro101 Aug 4 '14 at 15:09
  • This has now been posted and answered on Astronomy. – Philip Kendall Aug 8 '14 at 15:20