There's not a lot of information about this nebula. It seems to be a very photogenic, but forgotten denizen of the night sky.
Located in the constellation of Scorpius, a huge cloud of dust blocks out the light from a glowing cloud of energised Hydrogen gas located behind it.
The shape makes a viewer envisage a wolf, endlessly racing through space in pursuit of it's prey.
The nebula is catalogued as 'SL-17', and lies close to the nebulae 'Gum 55' and 'The Dark Tower'. There are a further 40-odd dark clouds that are denominated by the initials 'SL' in various catalogues. I doubt many of them are as attention-grabbing as this one.
Because of it's shape, the nebula is often referred to as 'The Wolf Nebula', or the 'Fenrir Nebula'. In Norse mythology, Fenrir (or 'Fenris') is a giant wolf of incredible strength. The son of Loki and the giantess Angrboda, Fenrir is the brother to Jormungandr (the world serpent) and the goddess of the underworld, Hel.
Unlike my attempt to image the 'Prawn Nebula', I had no technical problems this time. (I expect that Murphy will pay me a visit when I next try to image the night sky. We can only wait and see.)
I have resolved the guiding issues that I suffered from previously by the simple expedient of ignoring conventional wisdom and not balancing my mount slightly counterweight-heavy. The convention seems to be that for gear-driven mounts, you reduce backlash within the gears (by slightly off-balancing it) so that the gears have a constant load on them. Which is all well and good, except that my mount has a belt-drive system, so there is no need to keep the gears loaded. Now that I have started balancing my mount, I was able to achieve an average tracking error of 1 arc-second for all the time I was imaging SL-17.
The camera rotator that I bought has also been added to the mount's optical train. This allows me to keep the same camera rotation from one session to the next, and to alter the framing of the image to get a better aesthetic.
This image comes from 3 imaging sessions. Two long-duration sessions with the Optolong L-Enhance filter to capture the bright Ha background, with a short-duration session with the UV/IR-cut filter to capture the correct star colours.
Just to make things a bit more interesting, I imaged during the latest full moon. The general rule when using an OSC setup is "do not image a week either side of the full moon" because of the insane amount of light from the moon. (As an aside, when I was outside and my eyes got used to the light, I was able to see colours under the light of the full moon.)
All the data was stacked with 'SiriLic' and the basic processing carried out in SiriL. I used the new starnet++ integration feature to split the image into a 'starless' and 'stars' image pair before using Affinity Photo to recombine them into a single image for final processing.
Overall, I am happy yet unsatisfied with how my work came out. I feel that I can create a better image, but don't yet have the image processing skills to do so. I am particularly annoyed by the huge amount of noise introduced by starnet++, but am not able to do very much about it at the moment.
You are doing great Steve.
Re noise.
Can you drop your temp?
Do you dither?
Maybe try shorter exposures but lots of them.
Anyways you are doing great.
Excellent post.
alex
Great photo there Steveo! I do a fair bit of looking only through my newtonian and I dont think this has come up in my crosshairs. I had the same setup as yourself. The 183 is a great camera. I only ever added darks due to amp glow and used zero gain. Did you try a stack without flats and dark flats? I find that this works at times. And noise...I found more time will alleviate noise as you well know but you may have had some bad seeing conditions up top. Great pic mate.
Alex - I can drop the temp a bit, but have found zero to be a reasonable compromise. I do dither when imaging - just not very much - 2 pixels every 10 frames. (Which is fine when I'm doing 30-second exposures, but not so much in cases like this.)
Steve - I didn't try leaving out the Flats/DarkFlats as my Flats showed a fair few dust bunnies hiding in there. I might give that a try later today, too, and maybe see if Siril's 'drizzle' function can be accessed from Sirilic. I definitely keep the Darks because of the amp-glow - it's a pretty obvious with the '183.
Also, I tried using gain of 0 when I first got the '183, but suffered some seriously bad colour-banding across the image. I found anything under a gain of about 50 does this. How did you manage to use a gain of zero and not get the colour issues?
I didnt see colour issues using 0 gain(in my opinion..anyways) probably was. Im pretty wild with colour... I did use a filter..like yourself but the l-ultimate on nebulas. Maybe little effect, unsure.
I tried stacking without the Flats & DarkFlats. No joy - the dust bunnies made their presence known. I will have to invest some time and effort in eradicating them, again.
You can configure Sirilic to pass the 'drizzle' setting to Siril, so I'm now working with the output of that and will see how things turn out.
That’s a great image. I am using Siril also. So far seems good. But I am using a DSLR. I use the basic noise reduction module when still in linear data. Rob
Great pic V and a great target, props. You're really stepping it up. It's often hard to tell much technical from 200k but my guess is more gain and stretch less. In PI, an extra aggressive hyperbolic stretch gives you those puffy stars. Perhaps take the HDR hit of unity gain for the flexibility in processing, maybe.
Cyberman - Thanks! I usually do noise reduction later in the process, I hadn't thought of trying it with linear data before stretching. That might be worth a shot.
Oska - Thanks, too. I certainly don't feel like things are stepping up. I used a series of small GHS (General Hyperbolic Stretch) stretches in Siril, not one huge jump. Small steps seem to work a lot better. I'm not that far off unity gain (100 vs 110), so am a bit doubtful increasing the gain will make much difference - and also increases the risk of saturated stars.
I suspect that if I was to return to SL17 when there was no moon in the sky then I would have a better outcome. Imaging during the full moon (even with clear skies and an L-Enhance filter) is never optimal.
