#9: Second try on M101


M101 – 120sec subs @ ISO800

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 M101 versions


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,