The Horsehead Nebula in Orion

The Horsehead Nebula (also known as Barnard 33) is an iconic deep sky object located just south of Alnitak, the easternmost star of Orion's Belt. It’s part of the much larger Orion molecular cloud complex, and is in the southern region of the dense dust cloud known as Lynds 1630, along the edge of the much larger, active star-forming H II region called IC 434. The Horsehead is about 1375 light-years from Earth. It was discovered photographically in 1888 by Williamina Fleming on a photographic plate taken at the Harvard College Observatory.

This image uses H-alpha for the red channel, which gave better detail than the red data that I gathered. I shot the Ha data in 2016, with my scope on the old CPC fork mount, but it took me multiple tries over the next five years to get RGB data that I was satisfied with.

Exposure: Total exposure time about 20.3 hours. 45 x 20 mins Ha captured Oct-Nov 2016, 67:67:66 x 2 minutes R:G:B captured February 2022. All bin 1x1.
Light pollution: SQM ~18.38 (Bortle 7-8, NELM at zenith about 4.5, Red/white zone border.)

Seeing: FWHM of the integrated Ha data was 2.7 arcseconds
Image scale at capture: 0.6 arcsecs/pixel = f/5.7
Scale of presentation: 0.88 arcsecs/pixel (67% of original scale)

Equipment:
Scope: C11 (standard, not Edge) with Celestron 0.63 reducer
Mount: CPC1100 fork was used for the Ha data. For the RGB: 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, 5nm Ha and SII, 3nm OIII
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 3.1.0.558
Guide SW: PHD 2.6.9, connected to guide cam via native SXV driver
ASCOM: ASCOM 6.3.0.2831
Platesolving: ASTAP, failover to local Astrometry.net 0.19 server
Collimation: Metaguide 3, using ASI120MM connected via ZWO Direct Show driver 3.0.0.2

Processing Workflow by Workspace in PixInsight:

1. Calibration
Calibration with WeightedBatchPreProcessing with flats and bias, using Cosmetic Correction with a master dark
Blink to preview and reject a few frames

2. Stack and Mure Denoise
Image Integration on each channel
Mure Denoise on each channel
Dynamic Crop

3. Ha Linear Processing
Dynamic Background Extraction
Dynamic PSF
Deconvolution

4. Ha Stretching
Histo Trans x 2
Curves Trans
TGV Denoise to reduce fine-grained noise
Curves Trans

5. RGB Processing
ChannelCombination
Dynamic Background Extraction
Histo Trans x 2
Curves Trans
Linear Fit, using stretched Ha image as the reference
Replace R channel with stretched Ha = HaGB Image

6. Blending
Photoshop: Using a mask on the HaGB image, blend in the stretched Ha as luminance in the darker regions, with an opacity of 24%.
Pixinsight: Localized Histogram Equalization. I used various strengths to highlight different regions, then saved each image, and ported them back to Photoshop to blend together, using masks

7. Final
ICC Profile Transform to sRGB
Resample to 67% of original scale
Save as JPG