Wikipedia
In astronomy the Dobsonian is a type of Altazimuth mountalt-azimuth telescope mounttelescope mounting that became popular among amateur astronomers in the 1980s because of its extreme simplicity, low price, and rugged construction. The terms "Dobsonian" or "Dob" may also refer to any telescope that features this type of mount, although the telescopes themselves are typically of Newtonian TelescopeNewtonian design. on Dobson mount]]Although its namesake, John Dobson (astronomer)John Dobson, is frequently credited as having invented this mounting system in the 1950s, he does not make that claim. On the contrary, he points out that "for hundreds of years, wars were fought using cannon on 'Dobsonian' mounts." His innovation was in making large aperture telescopes affordable. Traditional mounting systems for large telescopes frequently cost more than the optical system they support. By grinding and polishing his own mirrors (frequently out of surplus porthole glass), and by constructing mounts out of little more than scrap building material, Dobson created what he called “sidewalk telescopes” for a fraction of the cost of commercial models. Scopes of this design tend to be very well balanced and have smooth operation, as well as being very compact, portable and easy to make. These features make the Dobsonian a favorite of amateur telescope makingamateur telescope makers. admiring an example of the telescope mounting system that bears his name]]The Dobsonian mount consists of three major parts. Azimuth (side-to-side) motion is provided by a turntable, on top of which sits a large box. Into the upper sides of the box are cut two semi-circular cutouts. Two disks are fixed to either side of the telescope tube at the balance point, and fit into the cutouts on the box to provide altitude (up-and-down) motion. The various bearing points are typically lined with teflon (although felt is also sometimes used) as a bearing surface.The entire mount is quite small in comparison to typical star-tracking systems, and can be easily transported. This has made it a favourite of amateur astronomyamateur astronomers because it can be carried to star partystar parties in the back of a small car and set up in moments. The result has been a fixation with ever-larger telescopes, which would otherwise require huge "traditional" mounts. Whereas a 8" Newtonian telescopeNewtonian would be considered large 30 years ago, today 16" systems are common, and huge 32" systems not all that rare.Dobsonians do have a few limitations. Because they are not designed to track objects, users must nudge the scope every few minutes to compensate for the rotation of the Earth to keep an object in view. This makes them less suitable for astrophotography and CCD imaging. They also tend to lack computer controls and GPS systems, thus requiring users to find objects themselves. But, what they lack in modern conveniences, they make up for in economy. John Dobson originally published instructions on how to make what came to be known as the Dobsonian telescope in his 1991 book ''How and Why to Make a User-Friendly Sidewalk Telescope'' (ISBN 0913399647), edited by Norman Sperling. The book treats the "why" as importantly as the "how", sharing Dobson's philosophy on the importance of popular access to astronomy for proper appreciation of the universe. Many other books and articles on the construction of Dobsonian telescopes have been published !since.Category:Telescopesde:Do bson-Teleskop