🩀 #21: Crab Nebula with Short Exposures & a Failed Polar Alignment on M81

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May 25, 2019 – M1 – 32 minutes total | 20s subs @ ISO 1600

⚠ New Lessons: Alignment Woes & Short Exposure Strategy

This session was meant to be a continuation of my previous attempt on M81 and M82 — to gather more data and improve the image quality significantly. That was the plan. What actually happened? A night of polar alignment frustration
 and an unexpected dive into M1, the Crab Nebula.

🔭 Image Acquisition

M81/M82 – Setup and Letdown

The setup routine was solid:

  • Leveled tripod and mount
  • Balanced gear
  • Polar alignment through the polarscope
  • SkyWatcher’s alignment refinement using two stars
  • Final one-star alignment near the target
  • Located M81/M82 and started the session

I reused the same imaging setup:
ISO 400 with 50-second subs — to match the data from the last session.

At first, things looked fine. But halfway through the night, I reviewed the frames — and every single one had star trails. Every. Single. Frame.
Polar alignment was clearly off, despite everything seeming to go smoothly.

The culprit? Likely the SkyWatcher alignment refinement. I’d already noticed that it gives different alignment errors depending on the stars you choose. One alignment star might give you a “great” rating, another might throw it off — even without touching the mount. This inconsistency makes it hard to trust. It’s a helpful system when Polaris isn’t visible, but for precision
 it’s unreliable.

Result: no usable data on M81 or M82 that night.
Frustrating.

🔄 Switching Targets – M1: The Crab Nebula

In a mix of frustration and stubbornness, I pointed the scope toward a random DSO from the hand controller’s catalog. It selected M1, the Crab Nebula.

The polar alignment was still off, so I made adjustments:

  • Reduced subs to 20 seconds (to avoid star trailing)
  • Cranked the ISO up to 1600 (the max on my Olympus E-510)

It’s a very noisy combination, but this was now a salvage mission.
One of the raw single frames looked like this:

đŸ–Œïž M1 Crab Nebula – single 20s frame @ ISO 1600

My plan: beat the noise by brute force. Capture a lot of short subs and let stacking do its magic.

đŸ§Ș Image Processing

I stacked 108 subs for a total of about 32 minutes of integration time.
Even with the short exposures and high ISO, DeepSkyStacker did its thing — reducing noise by averaging the chaos and letting the signal stand out.

The result?
Not pretty, but promising.

M1 is clearly visible, with faint structure and detail. The field is rich with stars, and despite the noise, it’s a real capture of the Crab Nebula.

I made two versions:

  1. Detail version – Noisy, color-muted, but M1 stands out along with the dense star field.
  2. Color version – Focuses on star color, but M1 turns a faint green and gets a little lost. Still interesting, but I prefer the first.

đŸ–Œïž M1 Crab Nebula – stacked result, 32 minutes total (+ stretched)
đŸ–Œïž Version 2 with enhanced star colors

🧠 Conclusion

A) Alignment matters. A lot.

SkyWatcher’s refinement tool is useful, but too inconsistent for my needs.
I’m now seriously considering a guidecam + PHD2 setup, which would allow:

  • Accurate polar alignment via drift or plate solving
  • Real-time guiding to extend exposure times
  • Plate solving for reliable framing

B) Short exposures + high ISO can work.

If your setup can’t handle long exposures, stacking lots of short subs is a very viable alternative.
Yes, it’s noisy.
Yes, it takes effort.
But noise averages out — and signal stays.
It’s almost alchemy: turning noisy frames into something worth seeing.

Another lesson learned. Another object imaged.
And somehow, despite the missteps
 it was still worth it.

Clear skies,
Chris