Tag Archives: truss

Bought a used 12″ Sky-Watcher Dobsonian Flextube Truss

12″ Sky-Watcher Flextube dobsonian with upgraded GSO dual-speed focuser

Well into my first month of my astronomy hobby, and I’m already on my 4th telescope gear: a 12″ Sky-Watcher Dobsonian with collapsible trusses. Standing next to my 8″ newt, it looks like a monster scope.

The Good
I believe I got a pretty good deal with this one because it has several upgrades including:

– dual speed focuser
– stiffer primary mirror springs
– smoother azimuth bearings
– swivel caster wheels under the base

and considering these were missing:

– eyepieces
– finder scope

The condition is almost brand new, no scratches on the base, and clean and shiny exterior. The primary and the secondary mirrors have some dust on them: an indication that they have never been touched. Then again, the average astronomer take extra special care of their telescopes. The total cost was “significantly” lower than a brand new one. But it cost me extra gas because had to drive 2 hours one way to pick it up.

First Challenges
Having spoiled by my Discovery 8 EQ in convenience/performance, I have to manage my expectations in order to overcome these challenges:

Heavy: Moving the telescope from my living room to the front door was easy because it had casters. Only when I had to disassemble and reassemble it outside that I realized how heavy and unwieldy this telescope was. I was expecting this before I bought it, but not as much as this.

Decollimated: I had collimated the scope inside, but when I reassembled it outside, it had miscollimated by a quarter of an inch.

Underfocussed: The upgraded dual-speed focuser was too short and extension tube was not included. I reached focus by pulling out the eyepiece by 30mm.

Jerky Tracking: Azimuth motion was very smooth, but altitude was quite jerky and squeeky making tracking and sketching more challenging than my GEM-mounted scope that had a smooth slow motion RA.

Foreground: New new (used) 12″ Sky-Watcher Flextube dobsonian. Background: My Discovery 8 EQ on hockey pucks.

First Impressions
First light was just outside my front door where I was subject to intense glare from my neighbours’ lights and street lights. The only way for me to judge the performance would be to take it to the same dark site where I have been taking my 8-incher. I might get a chance to do that this weekend.

In about a month, I will decide which one of my telescopes will have to go.