Here is my completed image of the Eagle Nebula (M16) imaged with Sulphur, Hydrogen, and Oxygen narrowband filters. This false-color widefield image of the nebula represents the strong oxygen signal as cyan, hydrogen as yellow/orange, and the stronger sulphur signal as red. Naturally, this nebula is nearly all red in color, as hydrogen-alpha dominates the field. With selective filters and processing I have stretched the intensity of the Oiii and Sii to better represent where they lie in the nebula.

Equipment:

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

Accessories:

DeepSkyDad Autofocuser

QHYCCD PoleMaster

Software:

SGP

PHD2

CdC

PixInsight

Acquisition:

Location: Flower Mound, TX for Ha(Bortle 7), Atoka, OK and Ft. Griffin State Historic Park, TX for Oiii and Sii(Bortle 3)

Dates: 5/12/18, 5/26/18, 5/27/18, 6/29/18, 6/30/18, 8/2/18, 8/3/18, 8/6/18

Gain: 200 Offset: 50

Camera temp: -10C

Sii: 36x600" Astrodon 3nm

Ha: 160x300" Astrodon 5nm

Oiii: 37x600" Astrodon 3nm

Total integration time: 25hr 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

LocalNormalization

ImageIntegration

DrizzleIntegration

DynamicCrop each master

DBE each master

Luminance Processing:

Duplicated the master Ha to use as the luminance

Deconvolution

TGV & MMT noise reduction (via Jon Rista's method)

HistogramTransformation bring to non-linear

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 F=0.2, (s=starless photo).

HDRMultiscaleTransform to reveal core

MultiscaleLinearTransform for sharpening

LocalHistogramEqualization

MMT and MT for star size reduction

MMT for noise reduction of the darker areas

Preparing separate Sii, Ha, and Oiii linear masters for tonemapping (applied to each master individually):

TGV & MMT noise reduction (via Jon Rista's method)

Removed stars via a StarMask and a few iterations of MMT and MT

Further removed background artifacts with an unmasked MMT

HistogramTransformation to bring to non-linear

HDRMultiscaleTransform to reveal core

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 colors to an aesthetically pleasing palette

CurvesTransformation for saturation

DBE to remove color bias in the corners

Combined Tonemap with Luminance using LRGBCombination

HistogramTransformation to stretch image slightly

UnsharpMask with a StarMask to harden up the soft stars a tad

CurvesTransformation for slight saturation

ACDNR for final noise reduction

Resampled to 40% for web posting