M42/43 once again

[wimvb]

I haven't imaged the Orion nebula that often, because of various reasons. For me it's a bit low in the sky and obstructed by a few trees near my observatory. This means that I would have to toss a substantial number of subs, of a sequence. Another reason is that this target is so common, that it doesn't offer anything new.

But, in 2021 I pointed my scope at this nebula for about half an hour and collected 72 30 s subs in R, G, and B. This is what I managed then

Processing this target is a challenge, and I've now procesed the data a number of times, as new tools have become available.

The newest kid on the block, for me, is GHS transformation in PixInsight. I followed Adam Block's YouTube tutorial and, in combination with Russel Croman's Blur- and NoiseXTerminator, this is the result.

The objective was to keep detail and colour right into the core, while showing as much as possible of the fainter regions.

After several passes of GHS, I almost got the nebula where I wanted it, but I found the core a bit flat. There's a lot going on near the Trapezium that I wanted to show. So, with a range mask exposing just the very core, I used MMT to add a little more local contrast in that area.

As I wrote before, the data consists of 72 subs of 30 s, with camera gain at its lowest, in order to keep the highest possible dynamic range.

Technical details:

SkyWatcher MN190 with ASI294MM camera at 0 gain and -10 C temperature, Optolong RGB filters

Exposure time: 30 s

Integration time: 36 minutes.

More subs might have given me more signal in the weakest areas, but I started to see horizontal banding in the image. Probably the exposure time is a bit too short (my normal exposure time at this gain is 300 s), and the read pattern starts to show. So I'm not sure if more subs or a higher gain would have made much of a difference. Using the high conversion gain of the camera would have reduced read noise, but it also would have reduced the full well depth.