Do you need a master dark flat frame? For me, I found that master dark flat frames worked better at removing electronic noise than bias frames.
Just like I need dark frames that match the environmental specifics of my light frames, I also need to have dark frames that match the environmental specific for my flat frames.
Unlike dark frames, dark flat frames will be much shorter, which means we are less concerned with amp glow. However, with short dark flat frame exposures, we can capture the electronic noise of our CMOS camera.
Additionally, you can also pick up a few hot pixels (pixels that are always on).
If we create master dark flat frames, like the one below, we can remove this noise from our images.
When you create a master dark flat frame, you can start to pick up the electronic noise pattern, which gets removed during image calibration. Unfortunately, all of this stuff changes based on exposure, temperature, gain, binning, etc., which means we will have a library of master dark flat frames.
Dark Flat Frame Library
For my equipment, I have 14 different dark flat frames for the following imaging conditions
- Narrowband: Gain 200 / Offset 50
- Duration:
- Hydrogen-Alpha Filter: 5.3 seconds
- Oxygen-III Filter: 3.6 seconds
- Sulfur-II Filter: 10 seconds
- Binning: 1×1
- CMOS temperature
- -30C (for winter imaging)
- -10C (for summer imaging)
- Duration:
- LRGB: Gain 139 / Offset 21
- Duration:
- Luminance Filter: .1 seconds
- Red Filter: .27 seconds
- Green Filter: .2 seconds
- Blue Filter: .22 seconds
- Binning: 1×1
- CMOS temperature
- -30C (for winter imaging)
- -10C (for summer imaging)
- Duration:
Dark Flat Frame Creation
For each master dark flat frame, I take 30 images. This takes 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 flat frame, I use the Image Integration process within PixInsight with the following settings:
These are the same settings I use for the Master Dark Frame creation.
What’s Next
The next step is to take the master dark flat frames and create master flat frames.