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If you are using dark frames, taking bias frames actually introduces noise.
1. Light frames contain the read noise, dark current and signal.
2. Dark frames contain read noise and dark current.
3. Bias contain read noise.
If you subtract the darks from the lights, you have removed the dark current and the read noise. If you then subtract the read noise again, you are introducing that same noise into the image again only inverse.
Your results look amazing. I've always wanted to make a barn door tracker. Was it hard to build?
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