Capturing Bode's and Cigar Galaxies: A Deep Dive into M81/M82

Astrophotography, while offering breathtaking views of the cosmos, often presents unexpected challenges. This post delves into the intricate process of capturing the iconic M81 (Bode's Galaxy) and M82 (Cigar Galaxy), sharing valuable insights and lessons learned from a recent imaging session.

The Project: More Than Meets the Eye

What might seem like an "easy project" for astrophotographers can turn into a complex endeavor. This particular imaging session, intended to be a secondary pursuit, proved to be a demanding one due to a combination of factors, including adverse weather conditions and processing hurdles. Despite setbacks, the experience provided a wealth of learning opportunities.

Equipment Setup:

• Scope: Askar 71F
• Guide Scope: SVBony 50mm
• Mount: HEQ5 Pro
• Camera: Player One Uranus-C
• Guide Camera: ASI120MM Mini
• Filter: ZWO UV/IR cut
• Accessories: ZWO EAF, SVBony Dew Heaters

Imaging Conditions:

The imaging took place under Bortle 5 and 6 conditions, with a total of 6 usable nights. Unfortunately, two nights were lost due to technical issues like "walking noise" and misaligned star rotation. The total integration time reached approximately 5.5 hours for the galaxy stack and 2 hours for a separate star stack, accumulated from captured data in April. Calibration involved 50 bias frames and 50 flats per night, with no dark frames used.

Software Suite:

A sophisticated array of software was employed throughout the acquisition and processing pipeline:

• Acquisition & Guiding: NINA
• Stacking: DSS (manual frame selection, stacking)
• Initial Processing: Graxpert (cropping, DBE, deconvolution, background noise reduction)
• Advanced Processing: Siril/Starnet/GIMP (platesolving, SPCC for color calibration, star splitting and recombination, background stretching, contrast and saturation adjustments, final cropping)
• Refinement: Seti Astro, Cosmic Clarity (star and background alignment, star stretching, final sharpening)

The Challenges Faced:

Several obstacles made this project unexpectedly tough:

• Terrible Spring Weather: High humidity impacted imaging quality.
• Star Overexposure: 120s exposures led to overexposed stars, requiring a separate star stack with shorter exposures.
• Camera Rotation Issues: Imaging stars twice was necessary due to incorrect camera rotation.
• Color Calibration: Achieving the desired colors proved difficult.
• "Walking Noise": This pervasive artifact ruined a significant portion of the acquired data.

Despite these challenges, the learning experience was invaluable, and the final result is a testament to perseverance.

Insights and Learnings

Camera Performance:

While the Uranus-C served its purpose, there's a noticeable performance drop at temperatures of 15°C and higher. Amp glow, though not expected, was observed at warmer temperatures. The camera's scaling also proved problematic, with darks taken at 20°C undercorrecting glow from lights at 22°C. A transition to a cooled camera like the IMX571 is being considered for improved stability and reduced artifacts. The sensor heater on cooled cameras also mitigates dew and frost issues.

Color Calibration with SPCC:

Siril's SPCC (Super Photo-Chemical Calibration) is highlighted as a powerful, free tool for achieving excellent color calibration, rivaling even paid software like Pixinsight in its effectiveness for RGB and narrowband data.

Dithering Strategy:

Dithering is crucial for breaking up pattern noise. A previous accidental configuration of one-directional dithering led to the loss of significant data. The current approach involves dithering every 4-minute subframe, or at least every 5 minutes, to ensure optimal noise reduction.

Autofocusing and Drift Correction:

NINA's autofocusing capabilities, particularly the "refocus after 10% change in HFD" option, are highly effective. The advanced sequencer's "center after drift" option is also a valuable tool for correcting tracking errors, especially during periods of poor transparency or seeing.

Reusing Flats and Darks:

To streamline the workflow and ensure consistency, the rig is not dismantled between sessions. This allows for the reuse of flats and darks (or bias frames), provided there are no significant changes in camera rotation or equipment. Having a cooled camera simplifies this laid-back approach.

Conclusion

Imaging M81 and M82 is a complex but highly rewarding undertaking. The journey from data acquisition to final processing is filled with learning opportunities. By understanding the nuances of equipment, software, and processing techniques, astrophotographers can overcome challenges and capture stunning celestial objects. We encourage feedback and critiques to further refine future imaging endeavors.