Dobsonian telescope

Dobsonian telescope. A typical design. A low-cost, large-aperture reflecting telescope on a simple, undriven altazimuth mounting. The design is suitable for visual observing by amateurs and is particularly portable. The name and concept derive from the pioneering work in the 1960s and 1970s by John Dobson of the San Francisco Sidewalk Astronomers. The telescope tube is typically square and constructed from plywood. The mount consists of a box, open at the top and on one side, which is mounted on a baseplate in such a way that it can rotate about a vertical axis. Semicircular cut-out yokes on the top of the box take large circular trunnions attached to opposite sides of the telescope tube (see illustration). The non-stick material Teflon is used to obtain smooth motion around the two axes. Dobson also demonstrated that a large mirror could be constructed cheaply and successfully from plate glass, which is thinner than a conventional mirror blank. The thin mirror needs to be supported loosely on a bed of carpet or foam rubber to avoid distortion.