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Contains:  Crescent nebula, NGC 6888, The star 34Cyg
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Crescent Nebula (NGC6888) imaged in SHO, 





    
        

            Andrew Klinger
Crescent Nebula (NGC6888) imaged in SHO

Crescent Nebula (NGC6888) imaged in SHO

Technical card

Resolution: 3153x2324

Dates:July 17, 2017Sept. 1, 2019

Frames:
Ha 5nm: 154x180" (gain: 200.00) -10C bin 1x1
Astrodon OIII 3nm: 58x300" (gain: 200.00) -10C bin 1x1
Astrodon SII 3nm: 56x300" (gain: 200.00) -10C bin 1x1

Integration: 17.2 hours

Darks: ~64

Flats: ~30

Bias: ~200

Avg. Moon age: 12.65 days

Avg. Moon phase: 24.35%

Bortle Dark-Sky Scale: 4.33

Astrometry.net job: 2909257

RA center: 303.714 degrees

DEC center: 38.703 degrees

Pixel scale: 2.878 arcsec/pixel

Orientation: 178.748 degrees

Field radius: 1.565 degrees

Locations: Atoka dark site, Atoka, Oklahoma, United States; Backyard, Flower Mound, Texas, United States

Data source: Backyard

Description

Here shown is a widefield view of the Crescent Nebula and surrounding nebulosity in the constellation Cygnus. In this false-color image Hydrogen(Ha) and Sulfur(SII) are shown as the warmer colors and Oxygen(OIII) is shown as blue. There are a few notable OIII structures that are not present in the other channels. Front and foremost is the shell around the Crescent nebula itself, and if you look to the top-center of the image you will see a perfectly shaped blue circle known as the Soap Bubble Nebula.

I recently captured the OIII and SII data to combine with my 2017 Ha data on this target.

Equipment:
OTA: William Optics GT81 w/0.8x reducer (382mm fl at f/4.7)
74mm aperture stop-down ring (brings scope to f/5.2)
Mount: Orion Sirius EQ-G (HEQ-5)
Guidescope: Orion 50mm guidescope
Guiding camera: Orion StarShoot Autoguider
Imaging camera: ZWO ASI1600MM-Cool

Accessories:
DeepSkyDad Autofocuser AF1
QHYCCD PoleMaster

Software:
SGP
PHD2
CdC
PixInsight

Acquisition:
Location: Flower Mound, TX (Bortle 7), Atoka, OK (Bortle 3)
Dates: 7/12/17, 7/18/17, 6/28/19, 9/1/19
Gain: 200 Offset: 50
Camera temp: -10C
Ha: 154x180" Astrodon 5nm
SII: 56x300" Astrodon 3nm
OIII: 58x300" Astrodon 3nm
Total integration time: 17hr 12min
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
DBE

Luminance Processing:
Duplicated the master Ha and Oiii to use as the luminance
Deconvolution on each Ha and Oiii
Created a synthetic luminance using PixelMath equation: "(Ha)+(max(Ha,(1.5*Oiii)))"
ArcsinhStretch and HistogramTransformation to bring to non-linear
ExponentialTransformation to push nebulosity
LocalHistogramEqualization
MultiscaleLinearTransform for sharpening
MorphologicalTransformation to reduce star size
UnsharpMask to harden up soft stars caused by previous step

Preparing separate Sii, Ha, and Oiii linear masters for tonemapping (applied to each master individually):
TGV & MMT noise reduction (via Jon Rista's method)
ArcsinhStretch and HistogramTransformation to bring to non-linear
Removed stars via StarNet++
DBE on the SII and OIII channel to help corners
LinearFit to Ha

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

Created an HOO image as well with this PixelMath formula (to blend later):
R: iif(ha>.15,ha,(ha*.8)+(oiii*.2))
G: iif(ha>0.5,1-(1-oiii)*(1-(ha-0.5)),oiii*(ha+0.5))
B: iif(oiii>.1,oiii,(ha*.3)+(oiii*.2))

SHO Tonemap Processing:
Invert > SCNR Green > Invert to remove magenta
CurvesTransformation to balance colors
Several a/b channel CurvesTransformations using ColorMasks to alter the colors to an aesthetically pleasing palette

HOO Tonemap Processing:
Invert > SCNR Green > Invert to remove magenta
HistogramTransformation to balance colors
CurvesTransformation to further balance colors

Combined SHO and HOO tonemap with PixelMath equation: "min(SHO,HOO)"
CurvesTransformation to brighten the image up a bit
SCNR Green

Combined Tonemap with Luminance using LRGBCombination:
Resampled to 35% for web posting

Comments

Author

ak_astro
Andrew Klinger
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Crescent Nebula (NGC6888) imaged in SHO, 





    
        

            Andrew Klinger

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