The Lobster Claw Nebula is large cosmic cloud around 11,000 light-years away. It’s mostly made from hydrogen, with some oxygen too, and is close to other deep sky objects.
Version 2, reprocessed December 2022
From the Reprocessing Bonanza 2022. This version uses exactly the same data as version 1, but with better processing tools and skills. Almost exactly six months separates the original with this reprocess. The original was fine but perhaps a tad too contrasty. I tried to apply a lighter touch this time around. Really, it needs a longer integration time. Always the way!
Version 1, June 2022
Having recently imaged four broadband targets, it was good to put my Optolong L-eXtreme filter back in and track down a narrowband nebula. The Lobster Claw is faint (as are most of the targets I image!) but a good size for my 400mm Askar FRA400 telescope and ZWO 2600MC-PRO camera. That combination gave me a wide enough field of view to capture other nearby deep sky objects in the same frame. Shout-out to the ASIAIR Plus‘ framing tool, which was very useful here.
It’s currently Summer, and although the skies don’t get properly dark until very late, if at all, I still find it’s worthwhile gathering data. (See Controversial Opinion #7). This particular imaging project took 20 nights, and most of them were cloudy. Even when the skies were clear, it was only dark enough for imaging between 11:30pm and 3am! Still, following my approach for getting long integration times meant that over those 20 nights I gathered over 30 hours of data, despite it being the peak of Summer in cloudy UK. Using PixInsight‘s SubframeSelector tool, I whittled down those 30 hours to the best 24.
Next came processing. I like PixInsight’s updated WeightedBatchPreProcessing, and the Execution Monitor that keeps you up-to-date with progress. It would be nice if it could include an estimated time to completion though. I know from experience that I’ll need to leave my PC number-crunching for around 24 hours, given the number of subframes I throw at it.
For the processing itself, I generally followed the steps outlined in this article. I did find that after recombining my L R G B images, the result was lacking in colour:
So, I went back to the R, G, and B frames. I wanted to push the B channel a bit more, but it was too noisy. The answer was to put it, along with the R channel, thorough the new NoiseXTerminator PixInsight plugin. This cleaned the noise up really well, and let me push the B channel a lot more, meaning that in the end I got more blue into the combined image:
Then there was another problem: there were several stars in the image with large halos. This is a side-effect of using the Optolong L-eXtreme. I took the image into Photoshop and cloned out the halos. See the slider image below for a before / after.
Then I did some more tweaking, and eventually produced the final image.
Close to the Lobster Claw is the better-known Bubble Nebula. It’s smaller, so wasn’t the main focus of my image. Maybe one day I’ll come back to it with a longer focal-length telescope. But it holds up surprisingly well when cropped in very tight, and works well as a bonus image!
Imaging details
* June 2022
* Bristol, UK (Bortle 8)
* Telescope: Askar FRA400 f/5.6 Quintuplet APO Astrograph
* Camera: ZWO ASI 2600MC-PRO
* Filter: Optolong L-eXtreme
* Mount: Orion Sirius EQ-G
* Guide: William Optics 32mm; ZWO ASI 120MM Mini
* Control: ASIAIR Plus, ZWO EAF
* Software: PixInsight, Photoshop, Lightroom, Topaz DeNoiseAI
* 720 x 120 seconds
Total integration time: 24 hours
By Lee Pullen
Example source data
Astrophotography is a pricey hobby, please help me out!
First of all, thank you for the information and the targets that you share with us.
I follow your workflow with good results and I have a question for you.
When you cloned out the halos of l-extreme in this photo and the artefacts of Starnet++, 2 bright stars on the top-right of the photo were cancelled. I think the same stars were also missing from the “stars-only” image because they are not in the final photo.
How you manage normally this issue?
I tried to draw a black point a bit larger than the core of the stars on the starless layer used to calculate the “stars-only” image but I don’t know if there is a better way (I haven’t Pixingight and I must use Siril and Affinity photo).
Best regards
Paolo
Hi, thanks for your message! Those two stars are missing from the final photo because I cropped very slightly to remove them for aesthetic reasons; I didn’t want very bright stars at the extreme edge of the frame.
Hi there, love reading your articles. You show real dedication in learning about some of your mpressive exposure times over multiple nights.
I have a much more simple rig and use an HEQ5 mount with Rowan belt mod, Skywatcher 72ED, ASIAIR PLUS, recently aquired ZWO585MC camera, 0.8x field flattener and Optolong L-Pro filter (I also have a 2″CLS).
I was wondering if you stack all your lights, darks, flats etc across multiple nights in one go, or do you stack images from each night, then ‘combine’ them in Photoshop? I use Deepskystacker and GIMP at the moment as they are free and relatively easy to use. I can’t seem to find any youtube tutorials on combining astro images for GIMP.
I look forward to your thoughts.
Many thanks,
Dougie
Hi Dougie, thanks for your message. I use PixInsight for my stacking, and throw all the data into one pot — that’s all my good quality Light frames across several weeks, along with Bias, Darks, and Flats. I’m happy that I don’t have to split the data by night, as that would take an age! I don’t use DSS or GIMP so can’t help you with that, unfortunately.