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M51 - The Whirlpool Galaxy in HaLRGB

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I originally planned on shooting this from a dark site on top of a mountain but my laptop had other plans. Ended up taking this from my driveway instead (at least when I still had a driveway), but I'm very pleased with the detail I got at just 610mm focal length. There are also a number of other galaxies in the uncropped pic including one over a billion light years away from us (calculated from redshift). This image was taken with a monochrome camera through filters for luminance (all visible light), red, green, blue, and Hydrogen-alpha (656nm), which were combined into a color image. The Hydrogen-alpha was combined with red (described below) to enhance the hydrogen nebulae in the galaxy (red splotches in the spiral arms). Captured on March 21, 22, 24, and 29th, 2021 from a Bortle 6 zone

Places where I host my other images:

Flickr | Instagram

Equipment:

TPO 6" F/4 Imaging Newtonian
Orion Sirius EQ-G
ZWO ASI1600MM-Pro
Skywatcher Quattro Coma Corrector
ZWO EFW 8x1.25"/31mm
Astronomik LRGB+CLS Filters- 31mm
Astrodon 31mm Ha 5nm, Oiii 3nm, Sii 5nm
Agena 50mm Deluxe Straight-Through Guide Scope
ZWO ASI-120MC for guiding
Moonlite Autofocuser

Acquisition: 10 hours 2 minutes (Camera at Unity Gain, -15°C)

Lum - 106x120"
Ha - 30x300"
Red - 40x120"
Green - 40x120"
Blue - 50x120"
Darks- 30
Flats- 30 per filter

Capture Software:

Captured using N.I.N.A. and PHD2 for guiding and dithering.

PixInsight Processing:

BatchPreProcessing
StarAlignment
Blink
ImageIntegration
DrizzleIntegration (2x, Var β=1.5) (Lum only)
StarAlign Ha, R, G, B stacks to drizzled L
DynamicCrop
DynamicBackgroundExtraction

Luminance:

EZ Decon + Denoise
ArcsinhStretch + histogramtransformation to bring nonlinear

RGB:

ChannelCombinaiton to combine monochrome R, G, B stacks into color image
PhotometricColorCalibration
SCNR green

Adding Ha:

I followed this tutorial which I find produces much better results than my previous NBRGBCombination script technique:

http://www.arciereceleste.it/tutorial-pixinsight/cat-tutorial-eng/85-enhance-galaxy-ha-eng

PixelMath to make Clean Ha. This effectively isolates just the Ha from the red continuum spectrum

Ha-Q * (Red-med (Red))

Q=1.0416

PixelMath to combine Clean Ha
PixelMath to add Ha to RGB image ($T)

R= $T+B*(Ha_Clean - med(Ha_Clean))

G= $T

B= $T+B*0.2*(Ha_Clean - med(Ha_Clean))

B=3

HaRGB:

Slight SCNR
HSV Repair
ArcsinhStretch + histogramtransformation to bring nonlinear
ColorSaturation to slightly desaturate Ha regions
HistogramTransformation to further stretch to match lum brightness

Nonlinear:

LRGBCombination with stretched L as luminance
Several CurveTransformations to adjust lightness, contrast, colors, saturation, etc.
MoreSCNR
ACDNR
LocalHistogramEqualization
More Curves
ColorSaturation to slightly desaturate Ha regions
MMT noise reduction
EZ StarReduction
Final Curves
Resample to 60%
DynamicCrop to 3555x2000
Annotation

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