Elephants Trunk Nebula HOO 2018

Elephant's Trunk Nebula, HOO, 2018

Interstellar dust and gas in the deep sky complex IC 1396 with the magnificent Elephant's Trunk Nebula. This is 4 hours of Hydrogen-alpha and Oxygen III.

Processing Details


StarAllignment of the linear Hydrogen-α and Oxygen III data using the Hydrogen-α frame as a reference.

DynamicCrop on both of them using the same process.

Background Noise removal with DynamicBackgroundExtraction (using 50 points on non-nebula areas).

Auto-stretch of the integrated Oxygen III frame with ScreenTransferFunction (STF), same auto-stretch on the integrated Hydrogen-α frame using HistogramTransformation to balance the emissions, as the emissions of the Oxygen III are weaker than the Hydrogen-α (the 'nebulosity' is stronger in the Hydrogen-α frame).

Noise reduction with MultiscaleLinearTransform. 4 layers with the following settings (R as default):

  • Layer 1: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 2: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 3: Threshold 0.500, Amount 0.50, Iterations: 1

  • Layer 4: Threshold 0.500, Amount 0.50, Iterations: 1

Star reduction with StarMask, 0.04000 Noise threshold, Scale 6 and 0, 1 and 2 for each Structure Growth property (Large-scale, Small-scale and Compensation) and 5 Smoothness level.

Final optimisations with CurvesTransformations and noise reduction again with MultiscaleLinearTransform using the same settings as above.


Selective Sharpening with High Pass Filter (radius 22.2).

Tech Card

Date / Location

24th December 2018 & 8th January 2019, Bedworth, GMT+0, United Kingdom, Bortle Class 5 ~SGM: 19.57 mag./arc sec2


Camera: ZWO ASI 1600MM-PRO USB 3.0 Mono (Type CMOS)

Sensor Cooling Temperature: -15C

Filters: 1.25" 5nm Astrodon Ha, 1.25" 3nm Astrodon OIII

Imaging Telescope: Takahashi FS-60CB

Correcting Lens: Takahashi Reducer 0.72x (composite focal length at 264mm and focal ratio at f/4.9)

Mount: iOptron CEM25EC

Image Quality

12Bit ADC (FITS)

Exposure time per image / number of composities and sensitivity

62 x 120" Ha subs (Gain 200, Offset 50/16, Binning 2x2)

44 x 120" OIII subs (Gain 200, Offset 50, Binning 2x2)

Total Integration Time

3hrs 32mins

Calibration Frames

25 Darks, 20/20 Flats for Ha/OIII


PixInsight 1.8 Core