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Astrophotography @lemmy.world lefty7283 @lemmy.world

NGC 1491 - The Fossil Footprint Nebula

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  • My last go at this nebula was back in late 2019, and I think I've gotten a little better since then (equipment is the same across both photos). The nebula in this pic is false color (SHO/Hubble palette), but the stars are true color RGB. Captured over a bunch of nights from January-April 2025, from a bortle 9 zone.

    Places where I host my other images:

    Flickr | Pixelfed

    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-290mc for guiding

    • Moonlite Autofocuser

    Acquisition: 70 hours 5 minutes (Camera at -15°C), unity gain

    • Ha - 123x600"

    • Oiii - 147x600"

    • Sii - 135x600"

    • R - 53x60"

    • G - 51x60"

    • B - 51x60"

    • Darks- 30

    • Flats- 30 per filter

    Capture Software:

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

    PixInsight Preprocessing:

    • BatchPreProcessing

    • StarAlignment

    • Blink

    • ImageIntegration per channel

    • DrizzleIntegration (2x, Var β=1.5)

    • Dynamic Crop

    • DynamicBackgroundExtraction

      duplicated each image and removed stars via StarXterminator. Ran DBE with a shitload of points to generate background model. model subtracted from original pic using the following PixelMath (math courtesy of /u/jimmythechicken1)

      $T * med(model) / model

    Narrowband Linear:

    • Blur and NoiseXTerminator

    • StarXterminator to completely remove stars from each the image

    • HistogramTransformation to stretch Ha and Sii images to nonlinear

    Broadband/RGB linear:

    • ChannelCombination to make color image from R G and B stacks

    • SpectrophotometricColorCalibration

    • HSV repair to fix blown out star cores

    • StarX (correct only)

    • StarX to make a stars only image

    • ArcsinhStretch + Histogramtransformation to stretch nonlinear (Calling this the Stars image now)

    • SCNR > Invert > SCNR (50%) > Invert to remove greens and some magentas from stars

    • Slight saturation boost

    Nonlinear:

    • ChannelCombination to combine stretched narrowband images into color image (SHO --> RGB)

    • Shitloads of curve transformations to adjust lightness, contrast, saturation, color balance, etc

    • LRGBCombination with stretched Ha as luminance

    • ColorSaturation

    • NoiseXterminator

    • LocalHistogramEqualization

    • Clone stamp to remove a couple highly saturated star spots that starx didn't remove (they looked incredibly out of place)

    • Pixelmath to add in the stretched RGB Stars image from earlier

      This basically re-linearizes the two images, adds them together, and then stretches them back to before. More info on it here)

      mtf(.005,

      mtf(.995,Stars)+

      mtf(.995,Starless))

    • DynamicCrop again

    • Resample to 60%

    • Annotation