| 8.75in F5.8 Truss Tube Truss Dobsonian |
| This is my first attempt at an ultralight scope. I was inspired by some of the scopes being built in the ATM community and very uninspired with my all too heavy dobsonian which required two sessions a week at the local gym to be able to carry it. So I set out with a number of goals in mind for an ulrtralight scope. Much of my motivation comes from the fact that I want to build a 20in Scope but had many ideas swimming around in my head screaming to be tried on a small scope first before delving into full scale war with my wife over the prospect of a monster sitting in the kitcken of my small flat in the centre of Edinburgh! 1. I wanted at least an 8in mirror. 2. No less than F5.5 to minimise coma 3. less than 8Kg for easy handling 4. Set up time of 5 mins. 5. All / mostly wood as I have no workshop or metal cutting facilities. 6. My cherry on top of my cake and eat it. |
| Scope details. The scope is an 8.75in F5.8 dobsonian. Mirror weight = 2.1Kg The total telescope weight is 4.9Kg. This weight includes my heaviest eyepiece, a 40 mm Plossl at 180g. As far as I am aware this is the lightest scope ever built in its class. |
| I spent a lot of time on the drawing board designing this scope. Manufactuing many of the parts proved to be very difficuilt without the use of a good workshop. However I am very pleased with the results and the scope performs better than expected. The motion is incredibly smooth, and I have experienced something that I have never even experienced in a manufactured scope - almost zero backlash. If I slew the upper end of the scope while viewing saturn at x169, there is virtually none. It moves exactly where I point it. I had a solid tube manufactured dobsonian scope and the backlash was about 20 arcmins. With this scope there is only about 40 arcsecs.. |
| Niggles and glitches There are however some flaws in operation that must be dealt with before this scope is user friendly. 1. Because the weight is so low, balance is a problem when swapping eyepieces. The scope is only tolerant of about a change of 75g at the top. 2. Because the scope is so light, focusing, can be tricky. 3. Probably a few more problems the more I use this scope! Wind does not seem to be as much of a problem as I thought. It blows through the scope! |
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| Main Design Features Azimuth locators are teflon pads, not sealed bearings. The truss tubes are themselves trusses. Spider cell is ultra-low profile Truss connector clamps are magnets - simple snap in action. Secondary cage is sandwich balsa-ply substrate with bonded sheet aluminium faces. |