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Highlands Astronomical Society

Dobsonian Telescopes

For those who crave larger apertures (a common astronomer's disease), but cannot afford an expensive fork mount to go with it, there is a very inexpensive alternative called the Dobsonian mount, named after its designer, John Dobson. The mount can only be used with Newtonian reflectors otherwise the eyepiece would not be easily accessible.

The Dobsonian mount is in effect a fork mount, although usually made out of plywood, fitted straight onto a base plate. There is no tripod or pier, making the mount very stable. Electric motors are now becoming available for these type of mounts, which would allow photography/imaging to be accomplished. A basic type of 'GOTO' is also available but is of the manual variety. Basic mounts have no slow motion controls and the scope cannot be used for photography, other than for very short exposures on bright objects.

Dobsonian telescopes are very portable and some use the open truss-tube contruction. This gives a weight saving by eliminate the need for a large heavy tube and makes it possible to disassemble the scope rapidly. This makes it (fairly) easy to transport telescopes with apertures of more than 40cm!

The disadvantage of using a large scope on a Dobsonian mount is that you sometimes need to stand on a step, or ladder, to reach the eyepiece, or sometimes you need to kneel down (when observing objects near the horizon.) A top section on the scope that can rotate helps to put the eyepiece in a more favourable position but again adds to the price.

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