#9: Second try on M101


M101 – 17x 120 second light @ ISO 800

New aspect: better polar alignment & comparing two cameras


The first camera I used was an Olympus E-5II. Then I had to change to an Olympus E510. This day I wanted to compare this two cameras by returning to M101. In the last weeks I had worked on polar alignment. Skywatcher offers a tool on their mounts to refine the polar alignment without a polar scope. In this procedure you slew to an alignment star and the mount will push this star out of the centre of your FOV. You then use the ALT/AZ knobs to recentre the star. Your polar alignment will then be refined. By fiddling with this tool I was able to refine the polar alignment in a way that makes 120 second exposures possible. Even on my small and overloaded mount like my Skywatcher EQ3 -Pro. I was quite impressed. Unfortunately something like half of the frames were wasted due to star stripes. But I tried my best and took a total of 40 x 120 second = 80 min. Cutting the ‘bad’ light frames out I was left with 17x 120 sec = 34 min of integrated exposure time on M101. Way to little for that tricky target. With 15 darks and 30 bias frames I tried to settle the noisy background.

Tech specs:

  • 17x 120 second light frames
  • 15 x 120 second dark frames
  • 30 bias frames
  • ISO 800


Even with a better moon phase then last time and doubling the exposure time I couldn’t get enough signal to work with. Like with the first version M101 only appeared as a needle peak on my histogram. Stretching this signal was a nightmare. Bloating stars, increased noise and a blurry target are the results. You can see the core, some structures in the arms but nothing that resembles the beauty of this galaxy.

comparing the latest version of M101 with my first try on that target


I need to come back once again. This time I need guiding, a dark moon, a light pollution filter, a decent camera and a hole night of exposure time. I want to capture this beauty in all its glory but that needs more equipment then what I currently own. A tricky one, a faint one… I’ll come back!

Greetings and clear skies,

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