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Picture

 

IC5146 Cocoon Nebula in (R+HA)GB and Re-processed NGC6888 Crescent Nebula in Narrowband Bicolour Palette

17/10/2018

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Despite appearances on the website and general workload, I continue to be pretty active, when the clouds allow. The past few days have been on and off due to a storm lingering around Spain, but thankfully I have been able to run my equipment for quite a few nights. I finished capturing data for my IC5146 Cocoon Nebula image, captured in (R+HA)GB. The end result is shown below. 
Picture
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I ended up capturing less Hydrogen-Alpha exposures than I originally wanted to. I was keen to finish work on the image and did not see much point in capturing the remaining 6 exposures when I already had 19 that were good. Towards the end, the nights were not as clear or reliable to continue imaging anyway. Since the Hydrogen-Alpha data was just used to enhance the Red channel, the 6 extra exposures would have not added much to the overall image. In summary, this image contains 50 exposures in Red, Green and Blue, all 15 minutes long. That plus 19 Hydrogen-Alpha exposures of 30 minutes each totals at 47 hours of exposure time in a single panel. 

I was also urged to re-process my NGC6888 Crescent Nebula in Narrowband Bicolour Palette image. I felt that the original image had too much cyan on the stars and too much noise reduction that made the image artificially smooth, with stars appearing to pop out. The re-processed image therefore has a lot less noise reduction, opting for more natural post-processing. I also managed to reduce the cyan colour of the stars. 
Picture
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→ View on Flickr
It is amazing what a seemingly small change to post-processing workflow can do to the overall image. I am much happier with this version. I find that at a long imaging focal length (I am currently imaging at 1592 mm), too much noise reduction makes the smaller stars appear to pop out unnaturally over the background. I am therefore increasing conservative about application of noise reduction to data.

​In the past, I have found myself post-processing a set of data multiple times and each time being happier with less and less noise reduction. Not that it is a bad thing, but it can be over-done very quickly. I would much rather look at an image that is slightly grainy in its small-scale noise than an image that looks artificially smooth. This applies both to my own images and images by other astrophotographers that I see online. 
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