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Been working on this again, still with old data. Loads of gradients that I can't seem to get rid of. I dumped a lot of [NII] subs that had rubbish stars, elongated and trailed.
TS 80mm f/4.4 six-element astrograph, 3nm Astrodons, ASI1600. I think I ran 5 min subs at max DR. Captured in Maxim DL processed in AstroArt5. Sigma Add stack, multiple gradient removals, ans several Histogram Stretch iterations.
Need more data. I have 2 hours of decent HII, but I want to add new [NII] and [OIII].
C&C welcome, and suggestions for further work. The JPEG looks nothing like the FITS I was working on, or how it looks on my monitor from Windows Photo Viewer. Pah!
90min HII, 72min [NII], and 80min [OIII] in 2 min subs with the 80mm f/4.4 and ASI1600 MMC camera through 3nm Astrodons. Piggy backed on the 130 f/7 mounted on the DDM60 and encoder guided.
Sigma Add stacking in AA5, then gradient removal, alignment and Trichromy with [NII] mapped to Red, HII to Green, and [OIII] to Blue, following the Hubble Palette.
Multiple Histogram Stretches, and a Low Pass filter to get rid of some of the noise. The RGB stack needed a serious crop as the [OIII] subs were at a steep angle to the other data, which is a pity as I can see plenty of outlying detail in the individual stacks.
I'm not taking this particular image any further as the data is too short. I've already got another 2 hours of HII in 5 min subs which I'll stack and add to the existing HII stack. The [OIII] I think I'll bin as it's so badly skewed, I'll try to replace it with 5 min subs properly aligned. The [NII] is OK as it stands, but I'll try to add to it.
When I'll be able to get more data is a moot point, as the weather here has been dire. There *may* be a couple of windows coming up, but I'm not counting on them.
I present Pickering's (Should be Flemming's) Triangle.
This is a combination of 2 hours HII and 2 hours [NII] as a mono image. I think this is valid as most NB filters pass both wavelengths.
Data was acquired in 10 minute subs with the 130mm f/7 TS Photoline triplet and APM / Riccardi 0.75x reducer working at 683mm, through 3nm Astrodon filters and an SX Trius 694 camera cooled to -30C. The telescope was encoder-guided on the ASA DDM60 mount with 120 point sky-model and local models for each run.
I already had 2 hour Sigma-Add stacks that had had gradient reduction (Adaptive Divide) applied to them so it was a simple matter to align and add them in AstroArt 5. The alignment borders were cropped off and another gradient reduction applied. Initial processing was using DDP, then two rounds of careful Histogram Stretch to push the background down a bit while brightening the highlights, with more gradient reduction in between each round.
I wasn't going to post this yet, but it looks like it may be a while before I can add to the data. The moon is starting to get in the way, especially in [OIII], and I'm back to school after the summer break so have to be up at stupid o/clock.
So here it is, The witch's Broom with 2 hours each of [NII], HII, and [OIII] in 10 min subs, mapping [NII] to red, HII to green and [OIII] to blue with no colour mixing between them.
TS Photoline 130mm f/7 triplet with APM-Riccardi 0.75x reducer, 3nm Astrodon filters, SX Trius 694 camera cooled to -20 C
Encoder- guided on an ASA DDM60 mount, Captured in Maxim DL6, stacking and processing in AstroArt 5
Stacked using Sigma Add, Bias only as the Flats I had were making things worse, as were the Darks
Each stack had Adaptive-Divide gradient reduction before RGB colour assembly, then cropped to remove alignment artifacts (Mostly in the [OIII] data collected after meridian flip) and another Adaptive-Subtract reduction before DDP processing. This was carried out very carefully to preserve the delicate tendrils of HII and [OIII] emission while avoiding burning too much out.
There were colour-noise artifacts in the background, which I reduced to some extent with Low-Pass Butterworth filtering, then finally used a little Histogram Stretch with curves to knock them down into the black while boosting the highlights a little, after another Adaptive-Subtract gradient reduction.
C & C welcome as always, and feel free to download the PNG and kick it around a bit if you want.