My Winter project shows the Sulfur, Hydrogen, and Oxygen emissions in and around the Orion constellation in a very widefield view. In this false-color modified "Hubble-pallet" I show the Sulfur and Hydrogen emissions as the warm red-orange colors and the Oxygen emissions as Blue. As a bonus, towards the bottom of the image you can see the Rosette and Cone Nebula pair in the constellation Monoceros.

In the Winter months, Even in the brightest cities, you can make out the large rectangle constellation of Orion with the 3 belt stars down the middle. In my image you can see the bright red star Betelgeuse at the bottom-left of the rectangle. If you can imagine just how large the Orion constellation appears to your naked eye you can see the sky is most certainly not empty! Some of the most popular nebula reside in this constellation, try to find the Orion Nebula (M42) and The Horsehead Nebula (IC434) sitting within all the dust.

When I was thinking of a target to shoot this last Winter, I really wanted to pair a widefield lens with my astronomy camera to capture the rich Hydrogen emissions around Orion. This is not new and has been done many times, usually in the form of HaRGB (using a Hydrogen-alpha filter to enhance a natural color image). A thought came to my mind that what if we were much further away from Barnard's Loop (the smile-shaped nebula) and were imaging it in narrowband. When imaging in narrowband, most nebula have strong Ha signal, moderate Sii signal, and faint diffuse Oiii signal. This combination creates those rainbow-esque images you often see from the Hubble scope. So where there is strong Ha signal, Sii typically follows, and I was puzzled why I could not find any examples of a wide narrowband view of Barnard's Loop. So after capturing plenty of Ha data I tried for some Sii exposures and to my surprise the signal was quite strong and showing up in a single exposure! So from that exposure I committed to going full SHO on Orion.

Now here is where it gets interesting (or maybe not). Oiii emissions were expected around M42, The Horsehead, and Rosette Nebula, were a pleasant surprise on the "head" of Orion (SH2-264), but completely unexpected as a large-scale diffuse signal around Barnard's Loop. With a discerning eye you can see in the individual Oiii channel a very diffuse background glow extending around and below Barnard's Loop. I know from my data that it was signal well above the noise floor, but I cannot say for certain that it is in fact diffuse Oxygen emissions until someone else goes after this widefield view with the same results.

View "Revisions" for channel examples:
A: SHO
B: SII
C: Ha
D: OIII
E: Ha - starless

Equipment:
Lens: Rokinon 24mm f/1.4 (stopped to f/4)
Mount: Orion Sirius EQ-G (HEQ-5)
No autoguiding used
Imaging camera: ZWO ASI1600MM-Cool

Accessories:
QHYCCD PoleMaster

Software:
SGP
PHD2
CdC
StarNet
PixInsight

Acquisition:
Location: Atoka, OK (Bortle 3)
Dates: 1/4/19, 1/5/19, 1/27/19, 1/30/19, 2/7/19, 3/5/19
Gain: 200 Offset: 50
Camera temp: -20C
Sii: 53x600" Astrodon 3nm
Ha: 42x600" Astrodon 5nm
Oiii: 43x600" Astrodon 3nm
Total integration time: 23hr
64x darks per calibration (master from library)
30x flats per calibration
200x bias per calibration (master from library)

Preprocessing:
Batch PreProcessing script to generate calibrated images
StarAlignment
LocalNormalization
ImageIntegration
DrizzleIntegration
DynamicCrop each master
DBE each master

Created a starless version of each channel using StarNet for use later in processing:
TGV & MMT noise reduction (via Jon Rista's method)
ArcSinhStretch x3
HistogramTransformation
StarNet

Luminance Processing:
Duplicated the master Ha to use as the luminance
TGV & MMT noise reduction (via Jon Rista's method)
ArcsinhStretch x3
HistogramTransformation
HDRMultiscaleTransform to restore M42 and Rosette
Combined the starless Ha image with the luminance using PixelMath expression "F=0.4; (1-(1-$T)*(1-s)*F)+($T*~F)" (s=starless photo).
Very small amounts of MMT noise reduction
HistogramTransformation
UnsharpMask
HDRMultiscaleTransform to reveal overblown parts of Barnard's Loop

Preparing the separate Sii, Ha, and Oiii starless images for tonemapping (applied to each master individually):
HDRMultiscaleTransform to reveal M42 and Rosette
HistogramTransformation

Combined prepared Sii, Ha, and Oiii masters with ChannelCombination:
R: Sii
G: Ha
B: Oiii

Tonemap Processing:
Invert>SCNR green>Invert to remove magenta
Several a/b channel CurvesTransformations using ColorMasks to alter the channels to an aesthetically pleasing palette
MMT for slight noise reduction

Combined Tonemap with Luminance using LRGBCombination
CurvesTransformation for slight contrast
CurvesTransformation saturation
MorphologicalTransformation for star size reduction
Resampled to 40% for web posting