I'm just catching up with the blog after a 4 clear night run where I was out every night. Actually my earlier posts of the Monkey Head Nebula and Horse Head actually made 6 nights straight of imaging and with Moonless skies.
I have imaged the Orion Nebula before at around the same time in 2022 and I'll do a comparison later. I tend to avoid it as to be honest there are so many great photos out there it's difficult to bring any new and at a basic level it is one of the easiest nebula to image being so bright. In fact that is one of the problems, it is so bright that the usual multiple minute exposures that are still required to bring out the faint details in the clouds simply burn out the centre. The trick I have learnt from watching this youtube from Trevor Jones is to take two sets of images, the usual longer exposure time for the details of the clouds and a second much shorter set, say 10s exposures (which you can take fewer of) to get the detail available in the core. The two images are pre-processed separately, before being combined using layer masks is Photoshop (other image processing tools are available...GIMP for example). The end product is known as a High Dynamic Range (HDR) image.
Find Orion using the 3 stars of his belt, from the left most star come South down the sword (pass the Horsehead nebula) and you will arrive at the bright "Great Orion Nebula", so bright that under suburban skies if you can see the sword then you will likely be able to make out the nebula as a hazy grey smudge with the naked eye. It has the designation of Messier 42 (M42), it is so bright it does make me wonder how it is not Mr Messier did not start with it! M1 is of course reserved for the Crab Nebula (a much fainter and smaller object). Around 1,300 light years away and surrounded by the Orion molecular cloud complex which covers the vast majority of the Orion constellation. It is fair to say that you could point a telescope and camera anywhere in Orion and come out with something of interest! In the very centre of the nebula is a very young open cluster known as the Trapezium, one of the major points of success for an HDR image is to be able to see those 4 stars that make up the Trapezium while still having the detailed cloud.
The plate solve of the image shows a rather cluttered mess of text. Mostly due to the number of objects in this frame outside of M42. The following annotated plate solve was provided by astrometry.net .
Capture
Jan 18th 2023, both sets of images taken in one session. I set up a slightly more complex advanced sequence within NINA to take the two sets of image, one of 10s exposure and one for 120s exposures, chose 120s rather than the normal 180s or even 300s as this is a bright object. I arranged the sequencer so that 2 long exposure images where taken then a single 10s, this was repeated until I lost the object behind the roof tops of neighbouring properties.
70 10s Exposures = 11m40s
139 120s Exposures = 4h38m
The ZWO ASI 533MC Pro was set to the usual gain of 100 offset 40 and running at -10ºC through the Optolong L-Enhance Filter.
The following morning I took 10s Darks at -10ºC and 120s Darks at -10ºC to create two new masters which are now in the library.
30 Flats and 30 DarkFlats where also taken - exposure to get a 50% histogram of 5.16s.
Pre-Processing
Two image sets where calibrated and stacked independently.
Processing 10s Exposures
After registration 69 Lights available
14 removed for FWHM - Aggressively used 3.5 as cut off point
0 For Roundness
0 for wFWHM
Leaving 55 of 69, 55*10s = 550s = 9m10s of exposure time
Processing 120s Exposures
After registration 139 Lights available
18 removed for FWHM > 4.0
0 For Roundness
0 for wFWHM
Leaving 121 of 139, 121*2m = 4h2m of exposure time
Post Processing
10s Exposures in Siril and Initial Stretch in Photoshop
Background Extract (RBF)
Colour Calibration Photometry Failed - not enough bright stars
Asinh Stretch - 3 iterations with stretches of (10,5,2)
Used Photoshop to perform a levels and curve stretches so that the trapezium stars were visible, as shown...
A close up of the centre reveals the Trapezium open star cluster.:-
This 10s stack was put to one side while the 120s images were Pre-Processed.
120s Exposures in Siril and Initial Stretch in Photoshop
Background Extract (RBF)
Deconvolution (Radius 1.0)
Colour Calibration Photometry Failed - not enough bright stars
Asinh Stretch - 3 iterations with stretches of (10,5,2)
Used Photoshop to perform a levels and curve stretches to get the nebula to a non-linear point with sufficient detail in the clouds not worrying about blowing out the core.
Photoshop Processing
As per the pre-mentioned tutorial from AstroBackyard, used Photoshop to create two layers with a layer mask used to blend the two images.
Raw - Highlights and Contrast
Raw - Texture
Raw - Clarity
Raw - Noise Reduction, small Noise and small detail enhancement
Raw - Saturation and Vibrancy and Shadow, small Sat, Vibrancy
Created Saved the overall workflow as a Tiff then exported final image to JPG and version for my Social feeds and Astrobin.
Results
I am very pleased with this image, not least because I used it to add another image processing technique to my toolkit. The blending of two images using layer masks is something that I will undoubtedly make use of again.
As a final compare and contrast last years image taken with the old Canon and more importantly my old rough and ready techniques!
