M42 – Orion Nebula – one year later

 Update! I’ve reprocessed the image:


The steps were mostly the same as before, but the HDR stage was tweaked a bit:

  • RGBWorkingSpace changed to 1 for each channel
  • DynamicPSF to generate PSF for Deconvolution
  • Luminance mask created from RGB image
  • Deconvolution used to bring out some more details
  • Multiple HistrogramTransformation runs to stretch the image carefully, and align the channels
  • HDRMultiscaleTransform with the brightest stars masked, once on the larger scale (~10) and once on a smaller scale (~7)
  • SCNR to reduce green
  • ACDNR to reduce noise
  • HistogramTransformation to stretch the image a little further
  • RangeMask+StarMask used to protect the background & bright stars
  • LocalHistrogramEqualisation used on the nebula to brighten things up
  • CurvesTransformation to increase contrast
  • UnsharpMask to sharpen some details slightly
  • Slight Convolution to reduce a bit of the harshness from UnsharpMask
  • ColourSaturation three times, one with a mask protecting everything but the brightest stars, one protecting the background and bright stars to increase saturation on the nebula, and once with the previous mask inverted to reveal some colour in the dusty background.
Original post:


I’ve shot this target before!

I haven’t done a HDR shot before, most targets don’t really need it in my experience. There is one huge exception – M42! The core of M42 is super bright compared to the rest, and then there’s the dust which usually goes unseen until you take much longer exposures.

M42 is easy to capture, hard to master.

General Details:
  • Date taken: 14/12/2014
  • Location: Adelaide, South Australia
  • Camera: Canon 450d w/ IR filter removed, GSO coma corrector
  • ISO800
  • Mount: HEQ5PRO
  • Scope: GSO 8″ f/5 Newtonian
  • Autoguider: Orion Starshoot AG
  • Imaging: BackyardEOS w/ PHD dithering
  • Guiding: PHD2
  • 50 bias frames, 20 dark frames (for the 300 second lights only!), 50 flat frames
  • 15 x 10 second exposures
  • 15 x 60 second exposures
  • 12 x 300 second exposures
  • Total integration time: 4650 seconds
Pre-Processing details (performed on each exposure length individually):
  • BatchPreProcessing, calibration only
  • BatchDebayer
  • Star Alignment with drizzle (took a lot of tweaking to get the 10 second exposures to align correctly!)
  • Blink to check for and remove any bad frames
  • Image integration with drizzle (using Winsorized Sigma Clipping)
  • Automatic background extraction on the three integrated RGB images to remove the light pollution
Processing the resulting RGB Images:
  • BackgroundNeutralization
  • ColourCalibration
  • SCNR to remove the green tinge
Prep the images for HDR:
  • StarAlignment of the three different integrations so they’ll line up
  • Blink to make sure they are lined up OK
  • DynamicCrop to cut out any bad edge bits
HDR Time:
  • HDRComposition to combine the three different exposure length integrations
  • RGBWorkingSpace
  • ACDNR to reduce noise
  • HistogramTransformation x2 to bring out the background dust
  • HDRMultiscaleTransform to reveal the core of M42
  • ColorSaturation to enhance the colours a bit
  • CurvesTransformation to enhance contrast and luminance
  • LocalHistogramEqualisation to brighten the image a bit

First Orion Nebula (M42) shot with my gear

Orion is a super easy target for beginners, and it is instantly recognisable in the night sky. This shot was taken without any guiding so I threw away quite a few exposures before I got something I was happy with.

This is a stack of nine 30 second exposures between ISO 400 and 800. The processing was done using DeepSkyStacker.


After stretching the image quite a bit, much more detail is revealed!


This is how my gear was set up taking these images – no autoguiding at this point!