Covering the telescope so no light enters, one would expect the image to be completely devoid of light. Yet, when I take a 10 minute exposure with a CMOS camera, I see things bright things.

This one image shows 3 things:

  1. In the top/bottom right corners, you can see a general brightness. This is amp glow. The longer you expose and image for, the more amp glow accumulates on the image.
  2. The random noise in the rest of the image is electronic noise from the camera.
  3. Abnormally bright pixels throughout the image (only a few) are hot pixels. These are pixels on the CMOS camera that are always on, regardless if they capture light.

If we create master dark frames, like the one below, we can remove this noise from our images.

Unfortunately, all of this stuff changes based on exposure, temperature, gain, binning, etc., which means we will have a library of master dark frames.

Dark Frame Library

For my equipment, I have 8 different dark frames for the following imaging conditions

  • Narrowband: Gain 200 / Offset 50
    • Duration: 600 seconds
    • Binning: 1×1
    • CMOS temperature
      • -30C (for winter imaging)
      • -10C (for summer imaging)
  • LRGB: Gain 139 / Offset 21
    • Duration:
      • 90 seconds
      • 120 seconds
      • 180 seconds
    • Binning: 1×1
    • CMOS temperature
      • -30C (for winter imaging)
      • -10C (for summer imaging)

Dark Frame Creation

For each master dark frame I need, I take 30 images. This will take some time, but it is something you can do during the day and not waste valuable darkness.

Once the images have been gathered for a master dark frame, I use the Image Integration process within PixInsight with the following settings:

What’s Next

The next step is to follow the same process but to create our master dark flat frames.