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6 Hour Witch's Broom


DaveS

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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

59a865129bd5e_6hourDDP.thumb.png.2488b93db0d6071093db7af0701ea0ab.png

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.

Phew!

C & C welcome as always, and feel free to download the PNG and kick it around a bit if you want.

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Thanks Martin. Yes, I was surprised myself at how much feint "fluff" there was, given the less-than-transparent skies I had. One of the joys of 3nm filters. I still want another 2 hours or so in each channel to improve the S/N ratio.

Regarding colour palette, I was somewhat restricted by not having PS to mix the channels (I may try the 16 bit Gimp I have), but also I wanted to go for a more "pure" "scientific" HST analogue.

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The [NII] is there, mixed in (In varying proportion) with the HII. Most of it is in the golden hues of the "fluff" under the blue [OIII] tendrils. There are some feint green HII tendrils there too.

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Looks very nice.  The palette is very unique.  I wouldn't say its green--which I usually eschew.  Its more greenish gold, like the first green leaves of spring--one of my favorite colors.  It definitely has the detail, and its very clear and clean.  Well done.

Rodd

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Thanks Rodd.

The colour balance is as it came out from the RGB combination, so I can't take credit for it, as much as I'd like to!

I think, that for my next round of subs, I may try pushing them to 1200 sec to see how the faint stuff comes up.

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