Sh2-224 - Supernova Remnant in Auriga [OC]

lefty7283@lemmy.world to pics@lemmy.world – 222 points –
live.staticflickr.com
5

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

Excellent work, thank you for sharing with us and please post more!

that 10-minute exposure image sure puts the work into perspective, if your amazing write-up wasn't clue enough already