Dobsonian
|
|
In astronomy the Dobsonian is a type of alt-azimuth telescope mounting that became popular in the 1980s for its extreme simplicity, low price, and rugged construction. Dobsonian may also refer to an amateur telescope that features this type of mount.
Invented by John Dobson in the 1950s (he called it a sidewalk telescope), it is a basic altitude/azimuth mount that does not follow the motion of the stars. It is therefore less technically advanced than most other mounts, but tends to be very well balanced and have smooth operation, as well as being very compact, portable and easy to make. It is a design favored by amateur telescope makers.
Dob-1.jpg
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 lined with several pieces of teflon (typically, 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 astronomers because it can be carried to star 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 would be considered large 30 years ago, today 16" systems are common, and huge 32" systems not all that rare.
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.