It feels ages since I last wrote a post on here, but looking back there’s actually been three this month alone! Hopefully the weather will keep on improving as we head into the depths of winter…Orion is calling me again!
The other evening we had clear skies, and even more surprisingly it was clear all night instead of just a couple of hours – I honestly can’t remember the last time it was clear right the way through ’til morning. To make things complicated though, a 94% illuminated moon was above the horizon throughout the night. Using my IDAS NBZ Dualband filter once again, with it’s 10nm passbands for both Hydrogen-Alpha and Oxygen-III, I was able to minimise the effect of the light pollution. The filter has honestly been a life-saver for imaging in my light polluted back garden, as well as under a full moon!
Also, it can be seen in the image above we have also had our back garden re-landscaped. Gone are the rocking slabs that used to move every time that myself, or the dog, used to go outside. Instead, they have been replaced by resin-bound gravel, which is one solid piece across the entire patio surface. I can now walk around the mount checking for cable snags, without introducing any noticeable guiding errors. This should help improve things a little bit!
Choosing a suitable target for the evening was quite an easy decision this time around – I needed a target that rose in the east and was visible all night long, yet wasn’t looking directly into the moonlight for the most part. I didn’t want to start embark on a new project, and the Cygnus wall is now setting in the west too early in the evening, so that only left IC1848 – The Soul Nebula. Previously, I only managed to capture 2 hours on this target and the amount of noise in the stacked image was utterly disappointing. It was a decent starting point, but it just lost most of the finer details in the nebulosity. My aim for this evening was to at least double the overall exposure time, if not more, and continue using 600-second (10-minute) exposures at ISO1600. This imaging plan seems to be working successfully with the NBZ, so why change it?
I decided to try a bit of an experiment while setting up; do I need to polar align using the in-built polar scope first, or just face the scope north and then use use the 3-Point Polar Alignment in-built within NINA. After a couple failed attempts due to not being 100% focused, it finally plate solved three different positions and as expected, I was way off – 10+ arc-minutes! By using the instructions and very subtle adjustments on the mount, I managed to get it perfectly polar aligned; within one arc-minute on both axis. I probably won’t repeat this next time, just use it fine-tune, but damn…it actually works!
I finally started imaging at 08:55PM and straight away my guiding was on point. Once again, the mount performed flawlessly, with the total RMS guiding never going above 0.7″. This means my stars were nice and round, even in the 600-second exposures.
The NBZ filter helped immensely with the moonlight, allowing the entire nebula to be easily seen in a single exposure. But what’s even more incredible is the guiding – below half an arc-second! I could have only dreamt of getting figures that low with my old EQ5 Pro! I’m still blown away by the AZ-EQ6-GT, every time I use it.
It got to around midnight, and after a successful meridian flip I felt confident to leave the sequence running for the rest of the night while I got some sleep, I had got work in the morning after all. I set it to image until 4AM, then park the mount and wait until I came out to replace the lens cap. However, when I came back inside and looked at the frames post-flip, there seemed to be a haze over the entire image. I can only put this down to three things:
- High clouds – This is doubtful though, as it was crystal clear all night.
- Dew on the mirrors or filter – It is possible, as the ambient temperature was near or below freezing.
- Moonlight – The most probable cause, as it was chasing Cassiopeia in the west when I came outside.
This is such a real shame, as it cost me over 2 hours exposure time; nothing was usable and every single frame had to be discarded. I suppose you win some and you lose some; it’s part and parcel of the hobby and you have to learn how to deal with it for next time.
Fortunately though, I still had 19 decent exposures, giving be a total of 3 hours 10 minutes from this single session. This means I achieved my aim to double my data on this stunning target.
Within Deep Sky Stacker, I stacked both the previous session with the new images, giving a total exposure length of 5 Hours 10m. Straight off the bat, after a quick stretch within DSS, the data looked extremely promising. There were a few stacking artefacts that would need to be dealt with, but quite easy to do with a simple crop and rotate within Photoshop.
However, once within Photoshop it was made evident that to pull the most out of the nebulosity, I would need to first remove the stars so I didn’t blow out any highlights. This can be done within a program called Starnet++, which for people that use PixInsight is all done in the box, however Photoshop hasn’t got that luxury. I managed to find a tutorial on how to install it as a separate piece of software within MacOS, and followed the step-by-step instructions within Terminal. After around an hour of fiddling with settings, I managed to get a suitable starless image of the nebulocity.
Back within Photoshop, it was then quite a simple task of stretching the the image and bringing out the really fine detail within certain sections. I added the stars back into the final image simply by using the original unstretched image on top of the layer stack. By using the blending mode on the original layer, I was able to add the stars back in, without reducing the details of nebula. Using this method, it has allowed me to keep the stars as small and tight as possible. I shall be using this method again in the future if the need requires.
The final image is one that I can say that I am honestly proud of! The stars are perfectly round, compact, and the diffraction spikes are nicely controlled, probably caused by not stretching them too much. And the detail in certain areas of the nebula are truly outstanding; most notably in the top left hand corner and the top half of the central lobe. It’s probably one of my best images to date!
And just for fun, I run this image back through Starnet++ to get a final starless image. This image clearly shows off the finer nebulosity interwoven between the two lobes and how far the dust stretches out.
As I said before, I hope the weather improves as we head towards the winter solstice and on into spring. Right now though as of writing this, we currently have 3 inches of snow in the UK and more on the way. So, I’ll have to wait and see if we have any more clear nights before Christmas! ‘Til next time, clear skies all!