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Propeller Nebula in H-alpha

Technical card

Resolution: 3700x2466

Dates: July 5, 2014

Frames: Baader Planetarium Ha 7nm: 12x900" ISO1600

Integration: 3.0 hours

Darks: ~30

Flats: ~30

Bias: ~50

Avg. Moon age: 6.92 days

Avg. Moon phase: 45.12% job: 791854

Locations: Backyard, Hampton, VA, Hampton, VA, United States


The Propeller Nebula is a faint H-alpha emission nebula that is often overlooked in the constellation Cygnus. This image was taken last July and even after 3 hours of exposure, it is begging for more integration time. I've tried on several attempts to acquire RGB data to make an HaRGB image, but clouds, dew and tracking all conspired to stymie those nights. Hence, I’m going to share what I've got and resume adding to this target next year when Cygnus returns to the summer sky.

Processing Workflow (PixInsight)

1. Calibrate light frames using darks, bias, flats
2. Superpixel Debayer, extract red channel.
3. Drizzle Integration using Winsorized sigma clipping rejection.

1. Non-linear stretch: set midtones to median image value (HistogramTransformation).
2. Non-linear stretch: set midtones to 0.8 (HistogramTransformation).
3. Non-linear stretch: lower black point (HistogramTransformation).
4. Non-linear stretch: increase midtones by lowering slider (HistogramTransformation).
5. Non-linear stretch: set midtones to 0.8 (HistogramTransformation).
6. Noise reduction (MultiscaleMedianTransform).
7. Compress dynamic range (MultiscaleMedianTransform w/lightness mask & star mask).
8. Noise reduction (GREYCstoration w/range mask protecting highlights).
9. Increase nebulosity brightness (ExponentialTransformation w/ range mask selecting highlights).
10. Increase small scale contrast (LocalHistogramEqualization w/ luminance mask protecting highlights)
11. Noise reduction (ATrousWaveletTransform, k-sigma noise thresholding)
12. Clean up dark pixels (Pixel Math [Shwartz script])
13. Increase contrast of propeller (LocalHistogramEqualization w/ range mask selecting propeller & brightest nebulosity).
14. Reduce star sizes (MorphologicalTransformation w/contour star mask)
15. Increase contrast (CurvesTransformation).
16. Lower background brightness (HistogramTransformation)
17. Even more noise reduction (ACDNR).
18. Final Crop (DynamicCrop)
19. Set ICC profile to sRGB for web publishing (ICCProfileTransformation).

Manfred Schwarz’ galaxy tutorial:



Jason Tackett


Propeller Nebula in H-alpha, Jason Tackett

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