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NGC6888 - experimental - last go at it this autumn

perfrej

By perfrej
in Imaging - Deep Sky

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perfrej

perfrej

Posted
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Good evening, folks!

I have been using NGC6888 as basis for improving my processing workflow and trying out some new stuff. I posted a version a while ago and that data is included in this one as well along with some more O3.

I look at this project as experimental. The colour rendition is experimental, as is the workflow in general, especially when it comes to getting rid of noise.

9 hours of Ha and 9 hours of O3, all in 20-minute unguided subs.

These were all shot at -20°C with a QSI-683 at the end of a TEC-140, which in turn sits on a GM2000HPS II, all housed in our remote observatory on Olly Penrice's premises, Les Granges, in Provence. No sleep was lost during the acquisition. Filters are from Astrodon (3nm O3, 5nm Ha). Capture with ACP/MaximDL/FocusMax, pre-processing in Nebulosity 3, registration, integration and base processing in Pixinsight, final tweaks in Photoshop.

I didn't have to do much in terms of processing. It is a bi-colour with Ha in red, O3 in blue, and Ha*O3 in green. Integration was done with averaged sigma rejection as that proved to increase s/n the most. I haven't worked with averaged sigma before; I usually do winsorized sigma.

Anyway, I leave this, along with a couple of vastly different renditions, behind me now and move into some galaxy stuff that I want to do as soon as the moon hides again and I get my focus motor taken care of.

Full resolution here: http://filer.frejvall.se/NGC6888-1101.png

/per

NGC6888-1101-1280.jpg

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perfrej

perfrej

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Thanks, folks! It is a very nice object, and the idea here was to get the O3 data in line.

Michael, next time you're there with your kids we'll throw on a 20°/s slew show! Like a 1930's circus show!

/per

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Barry-Wilson

Barry-Wilson

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Excellent Per - lots of fine wispy stuff all enveloped in a strong OIII shell.  First class.

I'm increasingly using TGVDenoise as a non-linear noise reduction tool (with ATWavelets in the liner stage) - which, and at what stage, did you use in the processing?  Out of interest, why did you calibrate in Nebulosity rather than in PixInsight with the Batch Preprocessing script?

BW

Barry

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perfrej

perfrej

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Kev, :)

Barry,

My noise reduction started very early in the process when I chose rejection algorithm. The difference was huge, and from now on I will always evaluate all three sigma-based rejections to see which yields the best result for the stack in question. I have yet to find a pleasing result from any of the noise reductions available in PI. The only one I used here was the built-in chrominance noise reduction of the LRGB combination thingy. After tweaking the channel weights a few times I switched to PS6 and did selective colour and a deep space noise reduction from Noel's actions. That's it. No more processing.

Nebulosity has a 7-pixel blur option for flats; an excellent option. PI's batch pre-processing doesn't really add anything but I intend to get to know it well enough to produce the results I want. Don't know how long it'll take ;)

/per

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