Link to inverted images
The Helix Nebula was discovered by Karl Ludwig Harding, probably before 1824. At 655±13 light-years (as measured by the Gaia mission), it’s one of the closest planetary nebulae to Earth. It’s about 2.5 light years across and about 10,000 years old.
Exposure: Total exposure time about 18 hours, 29:18 x 20 minutes Ha:OIII, 16:16:16 x 2 minutes R:G:B. All bin 1x1. Data collected in November and December of 2021.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)
Seeing: FWHM of integrated Ha and OIII images both around 3.05 arcsecs
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 1.2 arcsecs/pixel (50% of full scale).
Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: Paramount MX+, connected via ASCOM Telescope Driver 6.1 for TheSkyX, with MKS 5000 driver 6.0.0.0
Camera: SXVR-H694, connected via SX ASCOM driver 6.2.1.17140 (SX 1.2.2 also installed)
Filter wheel: Atik EFW2 with 7x1.25 carousel and Artemis 2.4.3.0 driver
Filters: Astrodon Type IIi LRGB
Rotator: Optec Pyxis 2", connected via Andy Galasso's 0.4 driver (Optec Pyxis Rotator AG)
Focuser: Rigel Systems GCUSB nStep motor with driver version 6.0.7 on stock Celestron focuser
OAG: Orion Thin OAG
Guide cam: Lodestar (first generation). 4 second exposures
Automation SW: Sequence Generator Pro 3.1.0.457
Guide SW: PHD 2.6.7, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.3.0.2831
Platesolving: PlateSolve 2, failover to local Astrometry.net 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver 3.0.0.2
Processing Software: Pixinisight, Affinity Photo, Photoshop CS2
Processing Workflow by Workspace in PixInsight 1.8.8:
1. Calibration
Calibration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
Blink to preview and reject a few frames
Weighting and registration with WBPP
2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
RGB Combination for RGB frames
Dynamic Crop
Dynamic Background Extraction
3. Narrowband Linear Processing
Deconvolution didn’t improve these images, so I skipped it
4. Narrowband Stretching
Histo Trans x 2
Curves Trans
Localized Histogram Equalization
TGV Denoise
5. RGB Linear Processing
Photometric Color Calibration, using Average Spiral Galaxy white reference
6. RGB Stretching
Histo Trans x 2
Curves Trans
TGVDenoise
7. Color Combination
Mapped HO(85% OIII + 15% Ha) to RGB for color
Curves Trans to boost color saturation
Color Mask script to create teal mask
Curves to shift core from green to blue, using the color mask
LRGB to create two images, one HaRGB and one OIIIRGB. The final image is mostly HaRGB, but in Photoshop I layered in the OIIIRGB in some areas where it enhanced contrast.
Mild LocalizedHistogramEqualization to enhance contrast in nebula
In the end I decided not to use the RGB star field, as it really didn’t add anything to the star colors
8. Background Subtraction
None needed in this image
9.
Final
Resample to 50% of original
ICC Profile Transform to sRGB
Save as JPG
