Dobsonian

A Dobsonian telescope is an altazimuth-mounted Newtonian telescope design popularized by John Dobson starting in the 1960s and credited with vastly increasing the size of telescopes available to amateur astronomers. Dobson's telescopes featured a simplified mechanical design that was easy to manufacture from readily available components to create a large, portable, low-cost telescope. The design is optimized for visually observing faint, deep-sky objects such as nebulae and galaxies. This type of observation requires a large objective diameter (i.e. light-gathering power) of relatively short focal length and portability for travel to relatively less light-polluted locations.

Dobsonians are intended to be what is commonly called a "light bucket" operating at low magnification, and therefore the design omits features found in other amateur telescopes such as equatorial tracking. Dobsonians are popular in the amateur telescope making community, where the design was pioneered and continues to evolve. A number of commercial telescope makers also sell telescopes based on this design. The term Dobsonian is currently used for a whole range of large-aperture Newtonian reflectors that use some of the basic Dobsonian design characteristics, regardless of the materials from which they are constructed.

It is hard to classify the Dobsonian Telescope as a single invention. In the field of amateur telescope making most, if not all, of its design features had been used before. John Dobson, credited as having invented this design in the 1950s, points out that "for hundreds of years, wars were fought using cannon on 'Dobsonian' mounts". Dobson himself identified the characteristic features of the design as lightweight objective mirrors made of porthole glass, and mountings constructed from plywood, Teflon strips and other low-cost materials. Since he built these telescopes as aids in his avocation of instructional sidewalk astronomy, he prefers to call the design a "sidewalk telescope". It appears that John Dobson simply combined all these innovations in a design that is focused towards one goal: building a very large, inexpensive, easy to use, portable telescope for the sole purpose of visual observing of astronomical objects as a way to bring astronomy to the masses.

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