Editing Dobsonian telescope (section)

== Derivative designs ==
[[File:Dobsonian rocker wood.jpg|thumb|upright|A modified Dobsonian from 1983 that features a collapsible open tube assembly with integrated bearing surface and a very compact "rocker box" mount.]]
[[File:Dobson truss.jpg|thumb|upright|Two Dobsonians that combine a truss tube, compact "rocker box", large radius altitude bearings, and a collapsible design.]]
From its inception, telescope makers have been modifying the Dobsonian design to fit their needs. The original design fit the needs and available supplies of one person—John Dobson. Other people devised variants that fit their own needs, abilities, and access to parts. This has led to significant diversity in "Dobsonian" design.

===Collapsible tube assemblies===
"Classic" design tube assemblies would require a large van for transport. Designers started coming up with disassembleable or collapsible variants that could be brought to the site with a small [[sport utility vehicle|SUV]], [[hatchback]], or even a [[sedan (car)|sedan]]. This innovation allowed the amateur astronomy community access to even larger apertures.

====The truss tube====
Many designs have combined the advantages of a light [[truss]] tube and a collapsible design. Collapsible "truss tube" Dobsonians appeared in the amateur telescope making community as early as 1982<ref>{{cite magazine |title=An Extremely Portable 17{{citefrac|1|2}}" Dobsonian |author=Hamberg, Ivar |magazine=Telescope Making |issue=17 |date=Fall 1982}}</ref><ref>{{cite web |url=http://web.telia.com/~u82002652/Galaxies/Obs/Dobson.htm |website=telia.com |title=The 17.5" Dobsonian |author=Hamberg, Ivar |url-status=dead |access-date=2009-02-25 |archive-date=2011-05-26 |archive-url=https://web.archive.org/web/20110526011517/http://web.telia.com/~u82002652/Galaxies/Obs/Dobson.htm }}</ref> and allow the optical tube assembly, the largest component, to be broken down. As the name implies, the "tube" of this design is actually composed of an upper cage assembly, which contains the secondary mirror, and focuser, held in place by several rigid poles over a mirror box which contains the objective mirror. The poles are held in place by quick-disconnecting clamps which allow the entire telescope to be easily broken down into its smaller components, facilitating their transport by vehicle or other means to an observing site. These truss tube designs are sometimes incorrectly called a ''[[Serrurier truss]]'', but since the main truss is not built with an opposing mirror cell truss it only performs one function of that design, i.e. keeping the optics parallel.

===Modifications to the altazimuth mount (rocker box)===

The main attribute of a Dobsonian's mount is that it resembles a "gun carriage" configuration with a "rocker box" consisting of a horizontal [[trunnion]] style altitude axis and a broadly supported azimuth axis, both making use of material such as plastic, Formica, and Teflon to achieve smooth operation.<ref>{{cite book|last1=Newton|first1=Jack|last2=Teece|first2=Philip|title=The Guide to Amateur Astronomy|url=https://archive.org/details/guidetoamateuras0002newt|url-access=registration|year=1995|publisher=Cambridge University Press|isbn=978-0-521-44492-7|page=[https://archive.org/details/guidetoamateuras0002newt/page/289 289]}}</ref> Many derivative mount designs have kept this basic form while heavily modifying the materials and configuration.

====Compact "rocker box" mounts====
Many designs have increased portability by shrinking the altazimuth (rocker box) mount down to a small rotating platform. The altitude trunnion style bearing in these designs becomes a large radius roughly equal to or greater than the radius of the objective mirror, attached to or integrated into the tube assembly which lowers the overall profile of the mount. The advantage of this is that it reduces the total telescope weight, and the telescope's balance becomes less sensitive to changes in the weight loading of telescope tube from the use of heavier eyepieces or the addition of cameras etc.

====Overcoming the limitations of the altazimuth mount====
Since the late 1990s many innovations in mount design and electronics by amateur telescope makers and commercial manufacturers have allowed users to overcome some of the limitations of the Dobsonian style altazimuth mount.

* '''Digital setting circles''': The invention of [[microprocessor]]-based digital setting circles has allowed any altazimuth mounted telescope to be fitted or retrofitted with the ability to accurately display the coordinates of the telescope direction. These systems not only give the user a digital read-out for [[right ascension]] (RA) and [[declination]] (dec.), they also interface with digital devices such as [[laptop]] computers, [[tablet computer]]s, and  [[smartphone]]s using live ephemeris calculating / charting [[List of planetariums#Planetarium computer software|planetarium software]] to give a current graphical representation of where the telescope is pointing, allowing the user to quickly find an object.<ref>{{cite web |url=http://orlygoingthirty.blogspot.com/2012/01/arduino-bluetooth-digital-setting.html |author=Andico, Orly |title=Arduino bluetooth digital setting circles for telescopes |date=January 11, 2012}}</ref><ref>{{cite magazine |url=http://www.jimsmobile.com/html_docs/ngc_review3.htm |author=Ward, Peter |department=Test Report |title=Digital Setting Circles Revisited – Lumicon Sky Vector I – JMI NGC-MAX – Celestron Advanced Astro Master |magazine=Sky & Space |date=December 1993}}</ref>
* '''[[Equatorial platform]]''': The use of equatorial platforms (such as the [[Poncet Platform]]) fitted under the altazimuth mount has given users limited equatorial tracking for visual and [[astrophotography|astrophotographic]] work. Such platforms can incorporate a [[clock drive]] for ease of tracking, and with careful polar alignment sub-arc second precision CCD imaging is entirely possible. Roeser Observatory, Luxembourg (MPC observatory code 163) have contributed hundreds of [[astrometric]] measurements to the [[Minor Planet Center]] using a home-built 20" dobsonian on an equatorial platform.