All About… Dobsonian telescopes

There is a lot of misunderstanding about Dobsonian telescopes; what they are and what they can do. This should help clear it up…

The Dobsonian telescope is a Newtonian reflecting telescope on an altazimuth mount. It is the mount that distinguishes it from any other type of Newtonian reflector and this was popularised in the Sixties by avid amateur astronomer John Dobson. It’s thought that Dobson invented the design for the mount, but as he freely admitted, the idea had been around for many centuries as cannons were mounted in such a way and wars fought using them. However, he developed the idea that Newtonian reflectors could be mounted on a simple platform using household parts and therefore very cheaply, and so his name was attached to the now ubiquitous amateur telescope.

It is their simplicity of design and cheap parts that made these telescopes so popular. There were many differing variations on the theme, some being very sophisticated and rather getting away from the humble and inexpensive materials and design. The popularity was quickly appreciated by commercial telescope manufacturers and so you can find Dobsonians as mass-produced products of varying size and quality, as well as in kit form.

Dobsonians are often known as ‘light buckets’ as they are an inexpensive way of owning a relatively large aperture telescope — most of the money you spend is put into the optics rather than the mount. In other words, the amount you pay for say a ten-inch aperture Dobsonian may only buy you a six-inch Newtonian on an equatorial mount. One of the advantages of the Dobsonian therefore, is the ‘bang for your buck’ in terms of aperture. When homemade, they are often built from plywood and other lightweight yet stable materials and usually disassemble easily for transportation and storage. Indeed, it is possible to have a 16-inch aperture telescope that fits into the back of a small family car. This means you can travel to a dark sky site and take advantage of it with a large telescope. They are, however, not suitable for some forms of observing.

Because the user has to constantly move the telescope to follow objects, observing anything at more than moderate magnifications can be awkward. Teflon bearings are used to give frictionless movement but there is still the inertia of the telescope to overcome. Dobsonians are not very suitable for anything other than basic astrophotography due to being on an altazimuth mount rather than equatorial. It is possible to get motor drives and ‘goto’ systems for ‘Dobs’ nowadays and even equatorial platforms, but this rather goes against the original idea of the Dobsonian telescope as being a cheap alternative for avid amateur astronomers.

The appeal of the Dobsonian telescope is unlikely to diminish any time soon, though, as they make a great introductory telescope for beginners and are ideal for experienced observers on a budget.

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