Eta Carina Mosaic Experiment

[AstroViking]

Hi all,

One feature of Kstars that I've been curious to try out is the 'Mosaic' feature, buried in the 'Sequencer' page. I watched a few YouTube videos so that I got an idea of how it worked and then decided to give it a try on the next clear night.

The selected Target? The Eta Carina nebula, of course. It's big, bright, and easy to find in the night sky.

I elected to use the 'stock' 420mm focal length of my telescope because I already had it configured within Ekos. The downside of this is the reduced field of view and the slightly elongated stars in the image corners. For the next mosaic I will prepare a bit earlier and use the flattener / reducer in the setup, and maybe drop the UV-IR cut filter in there as well. We'll see.

Also, the default 10% overlap is not enough - the stacking artefacts eat into this overlap and may make if difficult to align the panels. So I'll bump it up to 15%, or maybe even 20%, depending on what sort of FoV I have.

Because this was an experiment, I only took 90 frames for each panel - so about 22.5 minutes of integration time each. (The clouds were forecast to roll in at about the time I was going to finish. They didn't, but that's pretty usual for my luck when it comes to astro and the weather.)

I elected to do the stacking with SiriL, because it's the fastest and has very handy (and powerful) pre-processing tools. Each panel was stacked in SiriL, after which came a Background Extraction, Green Noise removal and a Histogram Stretch. Oddly, SiriL 1.0.6 has started crashing when I right-click the Background Extraction window to remove a sampling point. Not good, but given that SiriL 1.2.0 has entered 'beta' stage, I'm not overly worried.

The four stacked and pre-processed panels were loaded into Affinity Photo's Panorama tool and automatically stitched together. After cropping, I began the work of converting the very "dusty brown" looking output (see image V.1 below) into something that looked like an OSC image.

Image V.2 is a "mid-way" image, whilst V.3 is the final output. The colours are a bit over-saturated, I think, but are much closer to what my other images of Eta Carina look like.

For what it's worth, my working images were in the order of 70 megapixels (roughly 10,000 x 7000 pixels before cropping) and just under 900 megabytes in size.

As always, comments, feedback and constructive criticism are welcome!

Cheers,
V

Hardware: SW72ED @420mm / HEQ5-Pro / SV305+SV165 / ASI183MC-Pro / Kstars+Ekos

Image details:

* Gain: 50
* Offset: 10
* Temperature: 0 degrees C
* Exposure: 15 seconds
* Lights: 90 (22.5 minutes of data per panel)
* Darks: 50
* Flats: 50
* Dark Flats (Bias): 50
* Stacked and pre-proc'd in SiriL, then processed in Affinity Photo

[oska]

Nice one V, that's a great result for only 20 mins. And a 2x2 experiment!? Way cool! :cool2:
Have you looked at freebies like telescopius to post the full size?
How are you calculating exposure time?
The internal (eternal?) struggle with saturation seems to be a rite of passage? Quite often I'm finding my final tweak is to desaturate, sometimes quite a lot. It was definitely a surprise to me that I've had to fight it.

[AstroViking]

Hi John,

Thanks. Now that I (roughly) know what I'm doing, the next attempt will be a bit more serious. :thumbsup:

I used Telescopious to get an idea of how the image would turn out, but haven't looked at posting any images there. I haven't considered posting my work anywhere (other than here and on my website) because I don't think it's good enough.

When it comes to exposure times I take a series of frames, usually from 10 seconds up to about 60 and then eye-ball which exposure looks the best and not too washed out. In this case, I just recycled settings from my last Eta Carina image because I knew they worked.

When I do this again I will try for longer exposures, and maybe drop the UV-IR cut filter into the mix. According to the exposure time spreadsheet I've seen over on another (American) forum, I can bump it out to 20 second exposures.

The voices in my head are saying I should do two mosaics - one with the L-Enhance to boost the Ha and a second with the UV-IR cut and combine them. I'm trying to ignore what they're saying...

Oddly enough, I tend not to use the saturation controls when processing. This one was the exception to the rule. I've seen too many over-saturated images for my liking and don't like the way they look.

Cheers,
V

[Bodon]

Steveo, looks brillant! Glad you have the weather. Im sure that you next will be a ripper.

[oska]

I don't think you've over saturated, it's a very rich target. Working out what you like and then getting it is the struggle.
Listen to the voices, they're your wisdom, at least that's what mine said.