NGC 7000: A Journey Through Astrophotography Progress

Life happens, and sometimes our passion projects take a backseat. I've recently found myself navigating a particularly busy period with work and personal commitments, which has meant less time for capturing and processing the celestial wonders that I love. However, this lull also provided the perfect opportunity to reflect on my progress in astrophotography. I decided to revisit an object that holds a special place in my journey: the NGC 7000, also known as the North American Nebula.

NGC 7000 was the very first deep-sky object I ever attempted to image. Looking back at that initial effort, the difference between then and now is truly striking. While my initial processing, particularly my early experiments with the Hubble Palette (SHO), was admittedly a bit rudimentary, the most significant leap in quality comes down to a crucial piece of technology: the Electronic Autofocus (EAF). The sharpness of the stars in my most recent attempt is a testament to its capabilities.

Witnessing the Evolution

For those who are curious to see the progression firsthand, you can explore my early work and my latest capture through my Astrobin profiles:

My Very First Astro Image (2023):
My Most Recent Attempt:

It's incredibly rewarding to see how far I've come in such a relatively short period. The meticulous adjustments and the refinement of techniques have yielded a far more detailed and aesthetically pleasing result.

The Gear Behind the Image

Here's a rundown of the equipment used for this latest capture:

Telescope/Lens: Samyang 135 f/2 lens
Imaging Camera: ZWO ASI533MC Pro
Filters: Optolong L-Extreme Filter, Askar Color Magic SII-OIII, Optolong UV/IR Cut filter
Mount: Skywatcher Star Adventurer GTi
Autoguiding: Apertura 32mm Guide scope, ZWO ASI120mm Guide Camera
Control System: ZWO ASIAir Mini
Autofocus: ZWO EAF

Total Acquisition Time: Approximately 10 hours of light frames.

Processing the Nebula: A Deeper Dive

Processing this image involved a multi-step approach, especially given the use of different narrowband filters. Here's a simplified look at the workflow:

Ha-OIII and SII-OIII Separation: Using Siril, I applied its OSC HaOIII processing script twice. This process separates the Hydrogen-alpha (Ha) and Sulphur II (SII) data from the Oxygen III (OIII) data, resulting in separate files for each channel.
Sequence Alignment and Background Extraction: I then created sequences in Siril to meticulously align the stars across all four resulting files (Ha, SII, and two OIII files). Following this, a background extraction was performed on each file to ensure a clean base for stacking.
OIII Stacking: The two OIII files were stacked together to create a single, more robust OIII channel.
Color Combination (Pixel Math): Using Siril's Pixel Math function, I combined the processed channels into a color image. The mapping was Ha for Red, SII for Green, and the stacked OIII for Blue, following the SHO palette.
UV/IR Integration: Next, I created another Siril sequence to align the Pixel Math color image with the UV/IR cut filter data. This helps to improve overall image quality and color balance.
Star Removal and Stretching: StarNet was employed to remove stars from both the Pixel Math color image and the UV/IR data. This allows for independent processing of the stars and the nebulosity.
Advanced Stretches and Noise Reduction: With the starless images, I performed a series of Arcsinh stretches to bring out faint details, applied green noise reduction to mitigate unwanted artifacts, and utilized generalized hyperbolic stretches for further dynamic range enhancement. A touch of "salt and tequila" (a bit of artistic license and perhaps a late-night processing session!) was also added for good measure.
Star Merging: Finally, I merged the starless stretched Pixel Math image with the star mask generated from the UV/IR file, reintroducing the stars in a refined manner.

Ongoing Endeavors

While I'm pleased with the progress, there's always room for improvement. I'm currently experimenting with techniques to bring out more of the reds within the nebula, aiming for a more accurate and vibrant representation of its true colors.

Here's the final image:

NGC 7000 North American Nebula SHO