Friday, 12 March 2021

Varying Degrees Of Imaging Success

IC405, Orion and M51

I've been grabbing the imaging opportunities when I can of late.  The weather has been so hit and miss that it was nice to get at least something under my belt.   As I continue my imaging journey, I try to post all my images, and let's face it, a lot of them are rubbish.  Some are results of experiments with processing techniques and others are results are from different capture techniques.  Occasionally, it all comes together in a rather pleasing fashion.
So, I kick this little collection off with an experiment that didn't exactly go wrong, but was an interesting learning curve.  My first image is of the nebula IC405.  I have imaged this target before, but this is the first time I have done so using the quadband filter and the results are not entirely what I expected.  This might be down to poor understanding of the different light wavelengths emitted or reflected by the nebula, or an all out mistake somewhere in my processing workflow.  Whatever the reason, I have really struggled to get any significant colour to the target.
Otherwise know as the Flaming Star nebula, this is a completely different outcome to the last time I tried this.  The last time, I got plenty of blue, violet and red coming through.  This time, just a yellow or orange finish.  I might have to go back and reprocess using a different workflow on this one.

Next, we have an all time Winter favourite for visual observers and astrophotographers alike.  I've had a few goes at imaging the Orion Nebula over the years but as yet have not been able to get an image which I am truly happy with.  The search for the great image still continues.  However, there are mitigating factors for this image.  The thought of imaging in mono intrigues me, but I am firmly in the one shot colour camp at the moment.  And a lot of that has to do with time.  I simply don't have the time to spend taking upwards of 10 hours per image which is often required when using mono cameras.  My general mantra has been to use a capture time with a maximum of 3 hours, and OSC cameras allow me to do that.
With this image of Orion, I reduced that capture time even further producing this image with 6 x 5 minute exposures.  That was down to the great British weather.  The forecast says one thing, but nature decides on taking it's own course.  The tricky thing I find with Orion is producing something which doesn't blow the core of the nebula out.  It's such a bright target (visible to the naked eye under the right conditions) that it's easy to get carried away with getting as much detail as possible with the outer reaches of the nebula, but then lose the structure around the core.  Knowing that the final image was generally quite poor, I tried something a bit different by removing all the stars from the background.  The result, well, it shows some potential and one day I will nail that image of Orion.  Perhaps next Winter instead.

Eventually, when everything comes together I still continue to knock together something I'm genuinely quite pleased with.  M51 is a really pretty target.  A pair of interacting galaxies in the constellation of Canes Venatici and relatively easy to pick up and image with my 80mm refractor, M51 is instantly recognisable.  Other images I have seen of M51 always seem to have a pleasant blend of blues and reds in the arms of the main galaxy structure.  Traditionally, I have struggled to replicate this and I wasn't expecting too much different this time.  I wasn't sure how M51 would look after being imaged with the quadband filter so that was an unknown in itself. 
In the raw data, for some reason many of my subframes seemed to have horizontal banding across them.  I have read forums where other people have had the issue and have struggled to resolve it, but until now, I have never experienced it myself.  I hope that it's transient, one off in nature and doesn't start plaguing my imaging.  
I decided to use a workflow in PixInsight which starts off splitting the stacked image into different (R, G and B) colour channels, carrying out background extraction and then recombining them in slightly different ratios using PixelMath.  Towards the end of that particular workflow, I have learnt some new masking techniques which allows me to really enhance specific colours either just within the target, or the wider background.  
Anyway, 3 hours ish of subframes under near new moon conditions and then another 3 hours of calibration frames and few hours of processing have enabled me to put together this final image.

So there we are for another post.  Thanks for reading and clear skies!

Sunday, 28 February 2021

NGC 2244 The Rosette Nebula

 The Rosette in Quadband

Casting my mind back over the last 4 or 5 years, I try to remember when the last time was when I imaged NGC 2244.  The answer, well, I can't actually find any record of imaging it before which I suppose means that this is my first crack at it.  Usually, images of NGC 2244 are almost purely in red in appearance, but over the last year or so, I have favoured using the Altair Quadband filter.  This, in combination with continuing to learn new processing techniques in PixInsight as allowed me produce an image with a twist.
We're currently in a run of clear nights here in Herefordshire which also coincides with February's full moon.  Usually, this would mean slim pickings for both visual and imaging with a OSC camera areas of astronomy as the moon is so bright, trying to see anything is a tough ask.  But this is where the quadband filter really comes into it's own.
NGC 2244 is in the constellation of Monoceros and remains high in the sky for a great deal of the night, and is actually the designation given to the cluster of stars at the centre of the nebula.  To be more accurate, NGC 2237 is more commonly given to the nebula as a whole.
So, onto the image itself.  This image consists of around 3 hours of data made up of 5 minute exposures.  Then on top of that, approximately another 3 hours of dark frames, and finally the flat frames used for calibration.  The subs were all collected using Sharpcap and then the processing was done in PixInsight.  I think the absolute key thing with the processing workflow for this image in particular was being able to split the image into 3 colour channels (R, G and B) and then using a feature called PixelMath to re-blend those channels in different ways and I think this is the thing which has helped me to introduce the different colours to the final image.  To be perfectly honest, it really has surprised me when I see how it turned out.
Of course, with every image, there are positives and negatives.  Unfortunately after stacking the image using the calibrated frames to produce my base image, I saw that I had once again failed to deal with the amp glow and sensor noise which appeared in bands across the very top of the frame and the bottom of the frame.  I had put so much time and effort into getting the image that far, that I didn't want to start over and try to understand why my dark and flat frames hadn't removed all the regions of amp glow and noise they were supposed to so I decided to just crop the image to help improve the image.
Without further ado, here is the final image of the nebula, and I really look forwards to having a play with this data again to try and get even more detail out of it.

Thursday, 18 February 2021

A Horse and a Jellyfish

Good day to you and thanks for stopping by.  It's been a quiet start to the year in astronomy terms because of the weather.  Here in the UK, winters tend to be wet, wet and mild, wet and cold, wet and windy or very very occasionally clear and a bit chilly.  The common theme amongst most scenarios obviously being wet.  But for a couple of nights a week or so ago, we had several clear nights during which time I managed to get the roof off the observatory and get a few hours of photon collecting under my belt.  Over those evenings, I concentrated on 2 targets.  Both are reasonably common to amateur astrophotographers, but one of them was new to me.

Horsehead Nebula - Barnard 33

To kick off proceedings, let's take a look at my first effort.  The Horsehead nebula is in the constellation of Orion, and is often imaged in the same field of view as the neighbouring Flame nebula.  It's an area rich in Hydrogen Alpha, although the Horsehead itself is a dark nebula caused by what we think is a massive dust cloud in front of the dominant HA region.  As well as the Flame nebula and often overlooked, there is a third nebula in the vicinity designated NGC 2023.  This is a reflection nebula, quite small in apparent size and showing up in a blue white colour.

This attempt at the Horsehead nebula was a bit of an experiment (as you could argue are all my images!) where I used some new tools in PixInsight like the Game script, to try and really enhance the areas of nebulosity around the image.  This image is made up of 24 x 300 second images plus calibration frames all stacked and processed in PixInsight with some light touch ups in GIMP.

Jellyfish Nebula - IC443

My next images are of another nebula known as the Jellyfish nebula.  This is found in the constellation of Gemini.  It's one nebula in a massive area of nebulosity visible in much wider field images of the region.  IC443 is thought to be the remnant of a supernova which occurred circa 10000 years ago, although estimates range from 3000 to 30000 years ago.
I collected the data for these images during a night of particularly good quality seeing, and when ambient temperature was around -7 to -8 Celsius.  My Altair Hypercam doesn't have any TEC cooling, relying purely on a small fan to cool the internal workings of the camera down.  This means that I can never really cool the camera down much below whatever the ambient temperature is.  Therefore, the colder it is outside, the better the individual frames are being created by the camera.
In PixInsight, I generally use the same settings for pre calibration and stacking to give me a base image to start from.  After that, my workflow is somewhat less structured.  I have one workflow which I used for my OSC processing for quite a while with some reasonable success.  In more recent times I have started to use an Altair Quadband filter in my imaging train and I have started to experiment more with RGB and different palette techniques.  I have to remember that the likelihood of me being able to produce two identical images from the same base image using an identical workflow is incredibly small.  There are so many stages and steps that are subject to on the hoof interpretation, and so many little settings and sliders to tweak along the way that I'm far from knowing exactly what I'm doing at each stage.  Fun, isn't it?  Nevertheless, I can really appreciate the difference between these two workflows.
Both these images were created from the same master image composed of 78 x 145 second images (188.5 minutes total) plus calibration frames captured in SharpCap Pro.  Again, a majority of the processing was carried out in PixInsight with some final touches applied in GIMP.

The first of these images I produced using my standard OSC process.  There's plenty of colour to work with coming through, but the background stars really illustrate how much there is going in this region of the sky.

The second image is cropped slightly closer into the nebula and I have also managed to reduce the impact of the background stars (not exactly sure how though, but it'll be in the process somewhere).  I used a workflow which allows me to split the image into 3 channels (RGB) and work with them and mix them at different ratios using PixelMath in PixInsight.  I've also started to learn about some other masking techniques which I can use to help protect or expose the different areas of the nebula more specifically and enhance it.  The noise reduction steps in this workflow are also a bit different and appear to me to make a significantly larger difference.

I always enjoy my images, even if they never turn out great, but I particularly enjoyed working on the second of the Jellyfish nebula images.  Technique wise, I think it has got to be one of my best images although it's not the most stand out to look at.  I find myself looking back over the previous efforts and wanting to give them another go using the quadband filter in my newly developed workflow.  I just need the sky conditions to cooperate!
As always, thanks for reading, and clear skies.