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Astrophotography @lemmy.world
lefty7283 @lemmy.world
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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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