This week I kind of finished the 8″ dobsonian. Kind off, because I still have some things to do: balance is off, no dew protection, no primary mirror fan, lousy pivot bolt and too small a secondary mirror. But I wanted to test drive the scope before I worry myself about those details.
Yesterday was predicted to be a clear winter’s night. It wasn’t. It was extremely foggy. There were some clear spots so I decided to just start driving east. Well, I had to drive over 120km to find a spot that was clear: the Hessenweg between Apeldoorn and Kootwijk. It’s some 70 or 80 meters high and that was high enough apparently.
The enormous advantage of a ‘voll tubus’ dobsonian became clear to me after I set it up in 2 minutes. Setting up my previous truss dobson took about 15 minutes. Also this scope holds its collimation extremely well. I can literally bounce the scope in back of the car (involuntary….) and nothing bad happens. Good times! There and then I decided I was not going back to a truss dobsonian unless it’s a 20″ or bigger.
I aimed the scope at the Orion Nebula. For the moment I only have a 20mm eyepiece and with that Orion largely fits the FOV. M82 and M81 do fit the FOV. My old (Celestron?) 1.5x barlow was put to good use on the Sigar and I only slightly saw the darker ‘triangle’ in it.
M31 with its satellites where easily found thanks to the Telrad. Never used a Telrad before but it works superbly. Thanks to the DIY dew shield it also didn’t fog up, which was nice. However, on M31 I was confronted with the smaller aperture. In my 12″ Lightbridge and on a night like this a dark band would have been visible. Also it would have appeared much brighter. A minor disappointment but one that wasn’t a huge surprise as I already know what different apertures show.
The double cluster was used as a star test. At 60 times the stars where nice pinpoints of light. Going higher in magnification showed soft stars, especially when they were bright ones. That’s probably caused by my first time crappy collimation with a cheshire. Also the mirror coating is in a really bad shape (4 out of 10). I’m planning on having it coated again in March.
Things I learned about this scope:
- Need a proper collimation tool and experience with it;
- Balance issue isn’t that big of a problem;
- The grease in the focuser freezes up to easily and will have to be replaced.
All in all a successful test drive! And on the way back the added bonus of a huge boar on the side of the road. Nice!