Celestial hemisphere:  Southern  ·  Constellation: Sagittarius (Sgr)  ·  Contains:  Checkmark Nebula  ·  IC 4701  ·  IC 4706  ·  IC 4707  ·  Lobster Nebula  ·  M 17  ·  M 18  ·  NGC 6596  ·  NGC 6613  ·  NGC 6618  ·  Swan Nebula  ·  omega Nebula
The Swan Nebula (M17) and IC4701 imaged in SHO, Andrew Klinger
The Swan Nebula (M17) and IC4701 imaged in SHO
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The Swan Nebula (M17) and IC4701 imaged in SHO

The Swan Nebula (M17) and IC4701 imaged in SHO, Andrew Klinger
The Swan Nebula (M17) and IC4701 imaged in SHO
Powered byPixInsight

The Swan Nebula (M17) and IC4701 imaged in SHO

Equipment

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Acquisition details

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Description

Towards the core of the Milky Way in the constellation Sagittarius you would have to try very hard to not image some kind of nebula. In this image, M17, otherwise known as the Swan or Omega Nebula, lies in the upper right. Rich in Oxygen-III emissions, you can see the blues spilling out from the core. Towards the lower left of the image you can see the emission nebula IC4701. It is a much fainter and less often seen nebula which made it a challenge to display with its much brighter neighbor hogging up the dynamic range.

This false-color image represents the Hydrogen and Sulfur emissions as the warmer colors and the Oxygen emissions as blues.

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
PixInsight

Acquisition:  
Location:
Joshua, TX (Bortle 4) and Fort Griffin State Historic Site, TX (Bortle 3)
Dates: 6/21/22, 6/22/22, 6/23/22, 6/24/22, 8/25/22, 8/26/22, 8/27/22
Gain: 200 Offset: 50
Camera temp: -10C
Sii: 35x600" Astrodon 3nm 1.25" 
Ha: 258x300" Astrodon 5nm 1.25"
Oiii: 37x600" Astrodon 3nm 1.25"
Total integration time: 33hr 30min
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
ImageIntegration
DynamicCrop

Luminance Processing:
Duplicated master Ha to use as the Luminance
Deconvolution
ArcsinhStretch
HistogramTransformation
HDRMultiscaleTransform
Created a duplicate enhanced starless version using StarNet
Combined the starless version with the image using PixelMath expression "F=1; (1-(1-$T)*(1-s)*F)+($T*~F)". (s=starless photo)
LocalHistogramEqualization
MultiscaleLinearTransform
CurvesTransformation
StarNet to remove stars completely (this was decided later)

Preparing separate Sii, Ha, and Oiii linear masters for tonemapping (applied to each master individually):
StarNet
NoiseXTerminator
DBE
ArcsinhStretch
HistogramTransformation
ExponentialTransformation
HDRMultiscaleTransform

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

Tonemap Processing:
Many many Curves and Histogram Transformations with various ColorMasks to balance colors across the wide dynamic range of the image.

Combined Tonemap with Luminance using LRGBCombination:
Removed magentas with Invert>SCNR Green>Invert using mask
CurvesTransformation to balance background and colors
Added color stars by creating a star-only image from the original SHO data, removing greens, and blending using PixelMath screen operation.
Saturated and sharpened stars slightly
NoiseXTerminator
CurvesTransformation to balance background
Resampled to 70% for web posting

Comments

Sky plot

Sky plot

Histogram

The Swan Nebula (M17) and IC4701 imaged in SHO, Andrew Klinger

In these public groups

Narrowband imaging