M42 – The Orion Nebula, processed to be close to natural color. Sourcing from Dr. Roger Clark, the Trapezium core is green/teal reflecting oxygen emission, while the pink is from hydrogen emission. And the blue is reflection from the many hot, young blue stars in the area. 

In this photo, the total integration time: ~23 minutes (137 subframes at 10 seconds; ISO 1600)

Equipment: Sigma 150-600mm at a focal length of 600mm f/6.3 (95mm aperture) and a stock Canon 90D. However, as explained below, this is a crop from that original field of view. 

Skies: Haven't measured from camera, but presume about bortle 4 in Shenandoah NP, VA; taken mid-Nov. 2023.

Tracking: Fornax Lighttrack ii. No guiding.

Postprocessing: Light frames only (bias in rawconverter; darks not used, flats embedded in rawconverter). The light frames were calibrated in photoshop: adobe daylight balance+lens correction+ slight highlight and noise reduction).  Exported 16-bit TIFFs into DSS. applied a rectange box crop to enhance alignment, then stacked images. 

Rnc-color-stretch for sky glow removal and color preserving stretch in one-go, using v1.02 to pinpoint blackpoint.

Photoshop for additional curve work. Imagesplus64 for minor sharpening. Photoshop then used for changing color space from Adobe 1998 to sRGB and JPEG, then applied a final crop.

Flaws: The Sigma 150-600mm c, at least my copy, has serious aberrations on stars. This was noticed when focusing on the Nebula, with five different focus points failing to have in-focus stars across the entire field of view, therefore, focused on only getting semi round stars on the left edge of sensor. This is why I cropped a good bit of right side off prior to stacking to enhance alignment, and then cropped post-process to focus in on the main nebula, though it could be sharper without these issues.  There is noise present on outskirts of nebula, due to low total integration time. . Probably will not use this lens for astro going forward, will send in for evaluation to ensure nothing optically off. It is also possible that seeing also impacted stars as this was a hard test on lens.