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Astrophotography @lemmy.world lefty7283 @lemmy.world

Sh2-224 - Supernova Remnant in Auriga

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  • This is one of my longer projects, with 84 hours of long exposure time over 2 seasons going into this photo. Sh2-224 is an extremely faint nebula, and this is what a single 10 minute long exposure (through a Ha narrowband filter) of it looks like. I ended up getting ~83 hours of narrowband exposures like this, plus about an hour of RGB images for the stars. Because it's so faint, if the moon was up at all I did not shoot it, which cut the number of clear nights I could reasonably image it in half. The nebula itself is false color (although the HOO palette I used is fairly close to natural color), the stars were taken with RGB filters and are true color. With this project I finally managed to learn how to do some starless processing techniques for combining the stars+nebula

    Captured over 27 nights between February 2021 and April 2022, from my Bortle 6 driveway

    Places where I host my other images:

    Instagram | Flickr

    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: 83 hours 52 minutes (Camera at Unity Gain, -20°C)

    • Ha - 266x600"

    • Oiii - 231x600"

    • Red- 14x90"

    • Green- 14x90"

    • Blue- 14x90"

    • Darks- 30

    • Flats- 30 per filter

    Capture Software:

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

    PixInsight Processing:

    • BatchPreProcessing

    • SubframeSelector

    • StarAlignment

    • Blink

    • ImageIntegration

    • DrizzleIntegration (2x, Var β=1.5)

    Narrowband processing:

    • DynamicCrop

    • DynamicBackgroundExtractions

    • NoiseXTerminator

    • StarXterminator to completely remove stars for starless processing

    to be later replaced by RGB stars. doing this allows the nebula to be stretched without worrying about blowing out stars

    • HistogramTransformations to stretch nonlinear

    RGB Linear Processing:

    • DynamicCrop

    • DynamicBackgroundExtractions

    • ChannelCombination to combine monochrome R, G, and B frames into color image

    • PhotometricColorCalibration

    • Slight SCNR Green

    • HSV Repair

    super useful for putting color back into blown out star cores

    • StarXterminator to generate stars only image

    basically just getting rid of the background

    • ArcsinhStretch + Histogram transformation to stretch nonlinear

    Combining Channels:

    • ChannelCombination to combine stretched Ha and Oiii images into color image

    Ha mapped to red channel, Oiii to Green and Blue

    • HistogramTransformation to re-linearize HOO and RGB stars images

    • PixelMath to add RGB stars only image to starless HOO image

    HOO + Stars the math was simple

    • HistogramTransformation to bring HOO+Stars pic back to nonlinear state

    Nonlinear:

    • Shitloads of CurveTransformations to adjust lightness, saturation, contrast, hues, etc. with various masks

    • ColorSaturation to selective saturate/desaturate specific hues

    • More curves

    • Slight SCNR Green

    • NoiseXterminator

    • LRGBCombination with extracted L as luminance, used for chrominance noise reduction

    • even more curves

    • color saturation again

    • SCNR to remove some green star color

    • EZ star reduction

    • NoiseGenerator to add noise into reduced star areas

    • LocalHistogramEqualization

    • guess what baby more curves!

    • Extract L --> LRGBCombination again with mask for larger scale background chrominance noise reduction

    • Resample to 70%

    • Annotation