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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
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Crescent Nebula (NGC6888) imaged in SHO

Technical card

Imaging telescopes or lenses: William Optics GT-81

Imaging cameras: ZWO ASI1600MM-Cool

Mounts: Orion Sirius EQ-G (HEQ5)

Guiding telescopes or lenses: Orion 50 mm Guide Scope

Guiding cameras: Orion Star Shoot Auto Guider

Focal reducers: William Optics Flat 6A

Software: Sequence Generator Pro  ·  PHD2  ·  Cartes du Ciel  ·  EQMOD  ·  PixInsight

Filters: Astrodon OIII 3nm  ·  Astrodon SII 3nm  ·  Ha 5nm

Accessory: PoleMaster

Dates:July 17, 2017Sept. 1, 2019

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

Basic astrometry details job: 2909257

RA center: 20h 14' 51"

DEC center: +38° 42' 10"

Pixel scale: 2.878 arcsec/pixel

Orientation: 178.748 degrees

Field radius: 1.565 degrees

Resolution: 3153x2324

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

Data source: Backyard


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.

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

DeepSkyDad Autofocuser AF1
QHYCCD PoleMaster


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)

Batch PreProcessing script to generate calibrated images

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
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



Andrew Klinger

Sky plot

Sky plot


Crescent Nebula (NGC6888) imaged in SHO, 


            Andrew Klinger

In these public groups

Narrowband imaging