This summer I made a deep picture of the Dark Shark Nebula with my ASI 6200MM mono camera. It was a b&w picture, since I dont have RGB filters, and reflection nebula are difficult to see with the narrowband filters. Now that the 6200MM is away for repair I decided to try a deep color image with my Canon EOS R instead. For September it was a very warm night (+20C), so I expected (and got) much more noise in the images then with the cooled ASI 6200MM.
Here is what I have done
- - I took 117 images of 2 minutes in two days, of which 110 were usable
- - I also took 60 darks, flats and biases
- - I found that I got the best results without the darks. This is prove of what I have always heard, that its better not to apply darks if they dont have excactly the right temparture. The time would have been much better spent taking 60 additional lights.
- - I subtracted the bias master from the lights and the flats as it should be
For image processing I use Siril. After debayering, preprocessing, registration and stacking I did the following steps:
- - photometric color calibration to get the colors about right
- - background extraction, which also improved the colors at low intensity
- - histogram transformation
- - contrast limited adaptive histogram equalization (newly discovered feature in Siril, works great to enhance faint nebula)
- - export to tif format
The final steps were done in Rawtherapy
- - tone mapping, which I always use to reduce the dominance of stars wrt nebula (a kind of starnet++ light)
- - noise reduction
- - enhance blue light a bit in the channel mixer and with the blue RGB curve
All the processing was done on a Linux server with 8 CPU Cores and 32GB memory. Preprocessing, registration and stacking took 2 minutes each with 110 images. The whole processing took just about 30 minutes.
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