Heart Nebula (NGC896)
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12/21
ASI2600MC Pro, 44x 180s RGB (2.2h) + 21x 300s Ha&O (1.5h)
A part of the Heart Nebula IC1805 in constellation Cassiopeia. I've used additional data from a narrowband filter to enhance colors.
Even with the dual narrowband filter used in the above image, it probably resembles the visual appearence, as we would see it, quite well, since a color camera was used.
Hydrogen (H-Alpha, 656nm)
Imaging the same target with a monochrome setup and narrowband filters for Sulfur, Hydrogen and Oxygen, you may pick colors for those layers which differ from reality but emphasize the finer structures. This result is called a false color image and is common practise in technical and scientifical applications.
In astrophotography the so called Hubble resp. SHO Palette is pretty common. It maps the Sulfur layer to red, Hydrogen to green and Oxygen to blue. For my personal taste this is a little to harsh and I prefer to deviate from this slightly.
The same target may look like this, if colors and gradation curves are finetuned just for the most colurful result in mind:
I indeed used green for Hydrogen in this image, but I reduced that layer so only the brightest areas mixed with the red sulfur into yellow highlights. If you are interested how I combine narrowband data, check out the page From Mono to Color.
The images were captured using a fast f/2.8 telescope with a total exposure time of 9 hours. This is about 10 times more light compared to the above image with the slower optics. To get a similar result with the f/5.8 APO, about 40 hours exposure time would have been required.