The weather in my part of the UK, in fact I think this was the case across the whole country, finally cleared, 2 weeks of almost constant rain, wind and clouds. A safe bet of an object was required for the first outing in 2 weeks. I have tended to choose targets away from Orion for a couple of reasons, firstly everyone and their dog shoot it and some of the shots are particularly awesome. Secondly, the BrownsAstroGarden is a North facing with the house to the South. At my latitude this means that I only have around 2 months when it is accessible and then it is fairly low in the sky, just grazing the roof tops and I loose it after about 2 am. All that said, I decided to have a good go at the Horsehead and as way of a tutorial attempting to mimc a photograph by one of the public kings of the hobby Trevor Jones. You can see the look I was going for on the astrobin profile. There are lots to like about this image but I was interested in how to pull out the different colours between the Horsehead Nebula and the Flame Nebula. It maybe of course that Trevor is using LRGB and various other narrow band filters as part of this image and therefore the base data was very different to my Dual Band L-Enhance OSC capture. However, you'll see that my final image bares some resemblance albeit my colours are different (and perhaps a little controversial).
So the Horsehead nebula as you have probably already gathered is within the Orion Constellation, for Northern Hemisphere astrophotographers probably THE constellation. The Horsehead although visible with a large amateur telescope and good seeing conditions is I am told a testing subject to see visually. With a fairly wide field imaging kit such as my own it is actually quite straightforward to capture, the challenge is that the bright Orion's Belt star Alnitak always clips the highlights of the image. A number of other bright objects in the area meant that I thought I would change the 5m exposures I had been doing to one of 3 minutes.
The Horsehead Nebula refers to the dark nebula within the larger curtain of glowing Hydrogen rich gas formally given the designation of IC434. The Horsehead is about 1375 light years from us.
As you can see from the below image taken from Astrometry.Net, there are lots of other objects of interest in this one image.
NGC 2024 or the Flame Nebula is 1500 light years away, the glow of this nebula is the result of Alnitak's intense Ultraviolet radiation knocking the electrons away from the Hydrogen gas clouds and then recombining. As well as the Hydrogen gas there is plenty of dark gas and dust lying in front of this Hydrogen cloud which create the lines within it.
NGC 2023 and IC 432 are reflection nebula. NGC 2023 is a particularly large example of reflection nebula being around 10' square.
Capture
2023-01-16
Exposure at gain 100/ Offset 40, 180s at -10ºC, using the Optolong L-Enhance Filter and my ZWO ASI533MC Pro camera.
Lights - 123 (6h9m total exposure)
Darks - 30 (Creating a new master flat for this exposure time)
Flats - 30 (taken using a Trace Light Box)
Pre-Processing
Manually processed in Siril as per my Pre-processing workflow.
The following filters were used to reject registered lights:-
FWHM removed 13 > 3.6
Roundness removed 1 < 0.8
wFWHM removed 0 > 5 (seeing was good with No Moon during capture)
Out of 123 lights I was left with 109 for a total integration time of 5h27m
Post Processing
Siril
Crop - minor to remove 16 pixel border, snipping off the stacking artefacts
Rotated 90 and Vertical Flip, seems like a standard presentation of this object and given the square sensor I'm able to achieve this without any portrait / landscape orientation decisions
Background Gradient (RBF) - made a big change to the intensity of data across the 3 channels, until this point there was a very distinct green cast.
Colour Calibration Photometry
Deconvolution, Kernal size of 0.8
Asinh Stretch - 3 iterations with stretches of (30,10,2)
Histogram Stretch - auto-stretched
Green Noise Removal
Starless and Stars created using Siril Pixel Maths and Starnet++.
Once we have a TIFF (16 bit version) of Starless move into PS.
At this point I had this stacked image.
Photoshop (PS) Processing
My intention was to aim to bring out the different colours that exist in the Flame and the Horsehead Nebula as previously mention to aim for something like a Trevor Jones rendition of this image.
Basics of the processing was to take the starless image and using masking with significant feathering around each of the two major areas of the image (the Flame and the Horsehead Nebula). One by one a Mask was created around firstly the Flame Nebula following by the right hand quadrant over the horse head. I was then able to focus individual levels and curves on just that area, allowing for the flame to have the exaggerated yellow and the Horsehead into the reds and pinks.
Once those two areas had been adjusted then ran through my usual set of actions as follows:-
Levels & Curves - Careful here not to overly balance the channels, doing this initially resulted in a rather bland yellow fire not the raging red this nebula is known for.
Raw - Highlights and Contrast
Raw - Texture
Raw - Clarity
Raw - Colour Contrast
Raw - Noise Reduction
Raw - Saturation and Vibrancy and Shadow
I used the screen function in Photoshop to recombine the stars image, which is a little different than the PixelMath approach I normally take.
Created JPG and PNG versions.
Results & Thoughts
As you can see I went mad with my new technique (this is definitely only new to me, masking is a mainstay of any professional image editor). There is perhaps a tinge of "with great power comes great responsibility", and I think I have perhaps gone over the line here! I may revise the steps and come out with something a little less Ice Cream parlour. All that said, live and learn and I actually quite like the whacky palette, it brings something a bit different to the usual red tinged images you see from me.
Did I meet the brief of coming up with something along the lines of Trevor...MOSTLY NO, I certain have come up with a technique to process different parts of the image independently so that is a positive from this Post Processing session.
It looks like the clear skies and the moonless nights are going to hold for 1 or two more days here so a different target coming soon.
Clear Skies All.
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