NGC281 - Pacman Nebula

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The Pacman Nebula is a bright emission nebula in the constellation Cassiopeia.

Equipment:

  • Orion 8in F4.9 1000mm Newtonian Reflector

    • Flocked / Primary mirror replaced due to turned-down-edge

  • Skywatcher F4 Aplanatic Coma Corrector

  • Astrodon I Series 5nm Ha, 3nm Oiii, 5nm Sii narrowband filters

  • ASI183mm Pro cooled to -15C

  • Celestron CGEM Mount

    • Self tuned / hacks to get guiding stable include:

      • Intentional offset polar alignment so dec always pulses in one direction

      • Balance “west” heavy (rather than the recommended east) so that the ota “falls” onto the gear teeth rather than get “lifted”

      • Factor Reset hand-controller daily (to prevent cgem from being possessed and forgetting where the meridian is on subsequent night)

      • Dither in RA only

  • Data Acquired using N.I.N.A and Guided with PHD2

Acquisition Details (excluding rejected frames):

  • Ha: Best 36 of 40x10min (6 hours 00 minutes)

  • Oiii: Best 27 of 44x10min (4 hours 30 minutes)

  • Sii: Best 34 of 51x10min (5 hours 40 minutes)

  • Total: Bests 16 hours 10 minutes of 22 hours 30 minutes

The resulting image is a combination of the following steps:

  • Inspected all subs for bad images with Blink, discarding 40 subs due to clouds or otherwise poor guiding

  • Calibrated all subs with their corresponding master flat and master dark

  • Used subframe selector to weight Ha, Oiii, Sii separately for integrating each

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(20*(1-(FWHM-FWHMMin)/(FWHMMax-FWHMMin))

+ 10*(1-(Eccentricity-EccentricityMin)/(EccentricityMax-EccentricityMin))

+ 30*(SNRWeight-SNRWeightMin)/(SNRWeightMax-SNRWeightMin)

+ 20*(Stars-StarsMin)/(StarsMax-StarsMin))

+ 30

  • Selected the best sub from subframe and blink to use as a reference frame which stacking each set

  • Created a SNR Optimized Synthetic Luminance by integrating the three resulting stacks documented by Juan Conejero of the PixInsight Development team.

  • Cropped the stacking edges of the integrated masters

  • Linear fit the Ha and Sii images to Oiii for the initinal color balance

  • Combined the Sii as Red, Ha as Green and Oiii as the Blue channel to create a color RGB image

Luminance Processing:

  • Dynamic Background Extraction

    • 6 large points (Radius: 75 and 50)

    • Subtraction/Normalized

  • Automatic Background Extractor

    • Function degree 1 with normalization

  • Deconvolution was done on a separate copy of the luminance with

    • No deringing

    • wavelet regularization with 5 layers and strong but reducing amounts/thresholds

    • A starmask was created from a separate unmodified copy to replace the stars with the origional superluminance, eliminating the ringing artifacts from deconvolution as similarly documented by /u/OkeWoke

  • Noise Reduction was done using TGV Denoise with a low contrast mask and an autostretched local support and MMT with a very protective luminance mask

  • Combination of Histogram Transformation and Masked Stretch

  • Deconvolution with a star mask and Parametric PSF to tighten star cores

  • Morphological Transformation with a contours based star to shrink the overall intensity stars

  • Local Histogram Equalization - Two rounds at high scale with low amounts

  • S-Curve for overall contrast

  • HDR Multiscale Transformation - 6 Layers with a mask protecting the stars

SHO Processing:

  • Dynamic Background Extraction

    • 19 large points using Subtraction/Normalized

  • RGB Workingspace set to 1,1,1

  • Remove Magenta from SHO Stars (Invert+SCNR Green+Invert)

  • Noise Reduction using TGV Denoise with a low contrast mask and an autostretched local support

  • Noise Reduction using MMT with a very protective luminance mask

  • Morphological Transformation with a contours based star to shrink the overall intensity stars

  • Histogram Transformation to stretch to non-linear

  • Channel Combination in CIE L*A*B mode to add the Synthetic Luminance to the SHO color image

  • Additional Star Shaping with Morphological Transformation with Star Masks and Contours based star masks

  • Additional sharpening and noise reduction using ATrousWaveletTransform

  • Dark Structure Enhance script to bring out dark gobules throughout the nebula

  • Various curves to bring the Ha background to Brown, Soften the Green Overcast, and enhance contrast


Constructive criticism is welcome. Let me know what you think! How can I improve?