posted May 11, 2012, 12:51 AM by Mike White
(Originally posted May 3rd. 2012 6:02 AM by Michael Stapel)
The Dobsonian telescope mount has many great points, such as: it is easy to transport, easy and quick to set up, simple to operate, lowest cost per aperture (a.k.a. the biggest bang for the buck), a simple and robust design, intuitive to use, and more. Hurray I say!
However the height (off the ground) of the eyepiece can be a bit low when standing and repeatedly realigning the telescope, like at star parties. After a few great star parties resulted in a bit of a sore back afterwards, from the repeated stooping to realign the scope, my mind got to work on a solution..
Here it is.. a simple way how you can place the eyepiece higher off the ground: put the Dobsonian on a box.
Admittedly this can be tricky, because the point of gravity of the telescope will be higher off the ground. Extra care needs to be taken to ensure the complete setup does not become prone to toppling, that it is sturdy, and that it doesn't introduce vibrations.
The following setup works well for me. It has been trialled at several public star parties already. It works to satisfaction.
The "design" (ahem) is very simple: a sturdy box to raise the entire Dobsonian mount off the ground. The box shown here is actually an old kitchen drawer, left over from renovations of the kitchen. The drawer is 27cm high. The box construct as a whole, once feet and lid are added on, lifts the telescope up by about 32cm.
Rubber feet are attached to the base of the box, so it can sit comfortably on any surface. For stability three feet might be best, however my kitchen drawer did not support that setup. Instead there is one rubber foot on each corner, four in total.
To maximise the load-bearing capability of the feet and their mounting on the base of the box, additional pieces of wood were braced across the corners of the floor of the box, as shown on the photo to the left.
In case the box wobbles because it is placed on an uneven surface, a small wedge can be used to prop up one of the four feet, to stabilise the box.
A lid for the top of the box was made of wood, with some wooden beading on the underside of the lid to ensure it can't slide sideways. You wouldn't want the lid and the telescope to slide off the box whilst you're looking at Saturn!
Screwed to the top of the lid are three rubber cups, the kind often used to prevent furniture with coasters from rolling. They're used to securely retain the three feet under the base of the Dobsonian mount. These cups need to be positioned to fit the feet under the Dobsonian mount as precisely as possible, to prevent any horizontal movement.
Inside the box I placed two bricks (packed in bubble wrap) for extra stability and a lower point of gravity. Maybe this is not needed, but it seems a good idea to err on the side of caution :-)
This is basically it!
Here is the setup in action:
A few suggestions:
- stick a logo on the side of the box
- make a door in the side of the box, to store to eyepieces and filters (easy access!)
- screw a small spirit level to the lid
- plus all the ideas you've got that I haven't thought of!
Note: for most kids the eyepiece is now too high off the ground. This can be resolved with a small step ladder.