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


            Andrew Klinger
Crescent Nebula in HaRGB (NGC6888)

Crescent Nebula in HaRGB (NGC6888)

Technical card

Resolution: 3378x4498

Dates:July 25, 2017

ZWO B 1.25": 47x180" (gain: 75.00) -15C bin 1x1
ZWO G 1.25": 50x180" (gain: 75.00) -15C bin 1x1
Ha 5nm: 154x180" (gain: 200.00) -15C bin 1x1
ZWO R 1.25": 51x180" (gain: 75.00) -15C bin 1x1

Integration: 15.1 hours

Darks: ~64

Flats: ~30

Bias: ~200

Avg. Moon age: 2.32 days

Avg. Moon phase: 5.94%

Bortle Dark-Sky Scale: 4.00 job: 2052969

RA center: 303.727 degrees

DEC center: 38.704 degrees

Pixel scale: 2.015 arcsec/pixel

Orientation: 89.109 degrees

Field radius: 1.574 degrees

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

Data source: Unknown


This image shows the Crescent Nebula diving towards the larger structure that is part of the Gamma Cygni Nebula. The dusty red details throughout the image were captured using a hydrogen-alpha filter, while the star colors were combined in using RGB filters.

OTA: William Optics GT81 w/0.8x reducer (382mm fl at f/4.7)
Mount: Orion Sirius EQ-G (HEQ-5)
Guidescope: Orion 50mm guidescope
Guiding camera: Orion StarShoot Autoguider
Imaging camera: ZWO ASI1600MM-Cool


Location: Arlington, TX for Ha(Bortle 7), Atoka, OK for RGB(Bortle 3)
Dates: 7/12/17, 7/18/17, 7/19/17, 7/25/17
Gain: 200 Offset: 50 for Ha
Gain: 0 Offset: 10 for RGB
Gain: 75 Offset: 15 for RGB (experimenting)
Camera temp: -15C
Ha: 154x180" Astrodon 5nm
R: 51x180"
G: 50x180"
B: 47x180"
Total integration time: 15hr 6min
64x darks per calibration
30x flats per calibration
200x bias per calibration

Batch PreProcessing script to generate calibrated images
StarAlignment to register all frames to the reference
ImageIntegration (Linear Fit rejection)
DynamicCrop each master
DBE each master

Ha Processing:
TGV noise reduction (very slightly, via Jon Rista's method)
HistogramTransformation x2
Duplicated the image to create a starless version, using a starmask and several iterations of MMT and MT. Then pushed the faint nebulosity in the starless version using PixelMath expression: "1-(1-$T)*(1-$T)"
Combined the starless version with the image using PixelMath expression "F=0.4; (1-(1-$T)*(1-s)*F)+($T*~F)" followed by the same function but with a value of F=0.2. (s=starless photo).
HistogramTransformation to move black point
LocalHistogramEqualization with inverted starmask
CurvesTransformation for contrast using inverted starmask
DarkStructureEnhance Script

RGB Processing:
LinearFit to Red Channel
ChannelCombination to combine
SCNR Green
TGV noise reduction (via Jon Rista's method)
HistogramTransformation x2
CurvesTransformation for saturation
ColorSaturation tool to saturate blue stars more
CurvesTransformation using the ColorMask Script to saturate red nebulosity
MorphologicalTransformation for slight star reduction

Created HaRGB image using the script HaRVB-AIP
Script parameters adjusted as follows:
100% HAlpha in R Channel
33% R in HAlpha Channel
Noise It: 3
Transfer functions - Lightness: 0.6 , Saturation: 0.5
ChromaNR used with SmotherdWL: 3 and ProtectedWL: 2

SCNR Green
CurvesTransformation for contrast
Rotated 90deg and Resampled to 50% for web posting



Andrew Klinger
License: None (All rights reserved)

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Crescent Nebula in HaRGB (NGC6888), 


            Andrew Klinger