Monthly Archives July 2013

Sometimes Taking a Fresh Set of Dark Frames is Needed

Taking astro photos is a very noisy business so one technique to reduce the noise in your images is to take Dark Frames.  There are countless websites and blogs detailing the need and how to take dark frames but I am just going to focus on a visual example using the Eastern Veil Nebula (NGC 6992). I recently took 2 hours worth of data across 24 sub exposures in Hydrogen Alpha and I was so excited to begin processing it.  I was confused when my image, calibrated with Dark Frames and Flat Frames, came out very noisy!  I then began reprocessing to figure out what was going on.  It took me a while but then it hit me.  I was using an old master set of dark frames that I had only taken 15 dark frames with.  I then took a fresh set of 24 Dark Frames and that solved the issue, as you can see in the example below:

The image on the left was calibrated using 24 Dark Frames.  The image on the right was calibrated using only 15 Dark Frames

The image on the left calibrated with 24 Dark Frames. The image on the right calibrated with only 15 Dark Frames. The results are markedly different.

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