M16 Eagle Nebula: A Stunning Update with New Filters

M16 Eagle Nebula

I'm thrilled to share an updated capture of the M16 Eagle Nebula, a project that builds upon my previous attempt from two years ago. The original image, captured with an l-enhance filter and RGB stars, was a good starting point, but I was eager to incorporate SII data for a more vibrant and colorful rendition. This update was made possible by my new SII-OIII filter for my OSC camera.

While I acknowledge that combining OIII data from two filters with significantly different bandpasses isn't ideal, I believe the results speak for themselves. The enhanced color detail is quite striking, and I'm pleased with how it turned out.

The Challenge and the Reward

Returning to M16 is a project for another season, as capturing this target from my location presents unique challenges. The nebula barely reaches an altitude of 30° from my latitude, and my view of the southeastern sky is partially obstructed. This effectively limits my observation window to just a couple of hours per night.

Equipment and Technical Details

Telescope: SkyWatcher Quattro 200P with SkyWatcher 4 Coma Corrector
Mount: SkyWatcher EQ6R Pro
Camera: Touptek ATR2600C
Focuser: ZWO EAF
Guide Scope: 60 mm f/4 guide scope with ZWO ASI220MM Mini guide cam
Filter Wheel: Touptek 5x2" filter wheel
Filters: Optolong l-enhance filter, Altair 6 nm OIII-SII filter, Astronomik L-2 UV/IR cut filter
Powerbox: Pegasus Powerbox Advance gen2
Software: Mini PC running NINA and PHD2

Integration Time:

l-enhance: 162 x 180s = 8h 06m
OIII-SII: 176 x 180s = 8h 48m
UV/IR cut: 35 x 180s = 01h 45m
Total: 18h 39m

Calibration:

30x flats, 30x dark flats, master dark

Processing Workflow:

Processed in PixInsight, with l-enhance, OIII-SII, and RGB cut stacks processed separately.

Nebulosity Processing:

DBXtract script on l-enhance and SII-OIII stacks to separate out H, S, and O channels.
RGB Channel Combination using HSO palette.
BlurXterminator.
StarXterminator (discarding star image).
NoiseXterminator.
GHS in linear mode to adjust black level.
Split RGB Channels.
Seti Astro's Perfect Palette Picker script, picking SHO version.
Narrowband Normalization, SHO palette.
Curves Transformation to adjust colors and contrast.
Another light pass of NoiseXterminator.

Stars Processing:

Starting back gradient-corrected RGB master.
SPCC + background neutralization.
BlurXterminator.
NoiseXterminator.
StarXterminator (discarding starless image).
SetiAstro's Star Stretch script.
Curves Transformation to adjust saturation.
Pixel Math to recombine with starless.
Resample 50%.

Understanding the Colors

A common question I receive is about how filters contribute to the nebula's colors. In this case, all nebulosity data was captured through two different dual-narrowband filters.

Filter 1: Simultaneously captures Hydrogen Alpha (Hα) at ~656 nm (deep red) and Oxygen III (OIII) at ~500 nm (cyan, a mix of green and blue).
Filter 2: Captures Oxygen III again, this time in combination with Sulphur II (SII) at ~672 nm (even deeper red than Hα).

These two sets of data are then stacked individually and combined during processing. Since Hα and SII are both red, assigning them both to the red channel would lead to a loss of detail. To preserve the distinct information, one of the red wavelengths (Hα or SII) is assigned to the red channel, and the other is assigned to the green channel, while OIII is assigned to the blue channel.

In this specific image, I've used the SHO palette, also known as the Hubble palette. This involves assigning SII to red, Hα to green, and OIII to blue. This combination produces the distinctive, vibrant colors often associated with deep-sky astrophotography.

While I also captured a few hours of wideband filter data, it was exclusively used for enhancing the stars in the final image.

I'm excited to see what I can achieve with my monochrome camera on this target in the future! You can also view this image on .