A popular choice among amateur astronomers and home telescope makers alike, this Newtonian telescope design (popularized by John Dobson in the 1960’s) is an alt-azimuth mounted telescope famous for its simplicity of design. Dobson, an amateur astronomer who felt that astronomy should be open to everyone, created a design using plywood, formica, porthole glass and other everyday materials that could be built in someone’s back yard.
The Dobsonian design is intended for the visual observation of "deep sky" objects, a requirement which needs the astronomer to relocate to areas with little light pollution. Dobsonian telescopes are designed to capture as much light as possible from as few sources as possible, which necessitates their large diameter and long tube length. The large aperture design makes the dobsonian ideal for viewing deep sky objects such as star clusters, galaxies and nebulas.
The Dobsonian design is popular amongst amateur telescope makers for its simple requirements, and the design is being continually re-evaluated, remodeled and tested. Dobsonian telescopes are also popular among astronomers because of the large aperture, portability and low cost, all of which are necessary for the telescope to function properly. Although many companies manufacture commercial Dobsonian telescopes, building one of your own is considered a badge of honor among amateur stargazers.
In many ways, Dobson’s creation is merely an amalgamation of several dyed-in-the-wool astronomy techniques, rather than a new and original method of telescope construction. John Dobson has often claimed that he simply combined these earlier innovations into a design that helps take astronomy one step closer to his own overarching personal goal – making astronomy affordable and accessible to anyone interested. Describing it as a “sidewalk telescope”, Dobson took into account the fact that his telescope needed to be built from household items, and created several innovative methods of using the everyday junk in his telescope.
For the body of his first scope, for example, Dobson used a sonotube; a thick paper tube used to mould concrete pillars and columns. Instead of costly Pyrex lenses, he used old ship’s portholes ground down to fit into the tube, and for the mirror housing he constructed a simple plywood box.
The beauty of the Dobsonian design is that it can be set up anywhere, be it on the street as part of a sidewalk astronomy session, or up on an isolated hilltop miles from civilization. It is cheap to manufacture, easy to maintain, and eminently portable. In short, it is the ideal low-cost beginners-level telescope.
The Hubble Space Telescope