Editing Dobsonian telescope

{{short description|Type of Newtonian telescope popularized by John Dobson}}
[[File:Red dobsonian.jpg|thumb|right|A Dobsonian telescope on display at [[Stellafane]] in the early 1980s]]

A '''Dobsonian telescope''' is an [[altazimuth mount|altazimuth-mounted]] [[Newtonian telescope]] design popularized by [[John Dobson (amateur astronomer)|John Dobson]] in 1965 and credited with vastly increasing the size of telescopes available to [[amateur astronomy|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 observing faint [[deep-sky object]]s such as [[nebula]]e and [[galaxies]]. This type of observation requires a large [[Objective (optics)|objective]] diameter (i.e. [[Optical telescope#Light-gathering power|light-gathering power]]) of relatively short focal length and portability for travel to less [[light pollution|light-polluted]] locations.<ref name="books.google.com">{{cite book |url=https://books.google.com/books?id=l2TNnHkdDpkC&dq=dobsonian+amateur+telescope+makers&pg=PA286 |author1=Newton, Jack |author2=Teece, Philip |title=The Guide to Amateur Astronomy |date=19 January 1995 |page=287|publisher=Cambridge University Press |isbn=9780521444927 }}</ref><ref>{{cite book |url=https://books.google.com/books?id=9gUjaCMlX5oC&dq=dobsonian+amateur+telescope+makers&pg=PA37 |author=Ferris, Timothy |title=Seeing in the Dark |date=8 July 2003 |page=39|publisher=Simon and Schuster |isbn=9780684865805 }}</ref>

Dobsonians are intended to be what is commonly called a "light bucket".<ref>{{cite book |url=https://books.google.com/books?id=bmlIZHwuyvkC&dq=dobsonians+are+%22light+buckets%22&pg=PA74 |author=Allison, Mark |title=Star Clusters and how to Observe Them |date=21 December 2005 |page=74|publisher=Springer |isbn=9781846281907 }}</ref>{{efn|A light bucket is a telescope with a large aperture, used mainly for visual observing.}} Operating at low [[magnification]], the design therefore omits features found in other amateur telescopes such as [[Equatorial mount|equatorial]] tracking. Dobsonians are popular in the [[amateur telescope making]] community, where the design was pioneered and continues to evolve.<ref name="books.google.com"/> A number of commercial telescope makers also sell telescopes based on this design. The term ''Dobsonian'' is currently used for a range of large-aperture Newtonian reflectors that use some of the basic Dobsonian design characteristics, regardless of the materials from which they are constructed.<ref name=levy/>

==Origin and design==
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.{{citation needed|date=July 2018}} John Dobson, credited as having invented this design in 1965,<ref>{{cite book |url=https://books.google.com/books?id=Thgzo8q3GJUC&dq=dobsonian+amateur+telescope+makers&pg=PA351 |author1=DiBona, Chris |author2=Stone, Mark |author3=Cooper, Danese |title=Open Sources 2.0 |date=21 October 2005 |page=351|publisher="O'Reilly Media, Inc." |isbn=9780596553890 }}</ref> pointed out that "for hundreds of years, wars were fought using cannon on 'Dobsonian' mounts".

Dobson identified the characteristic features of the design as lightweight objective mirrors made from [[porthole]] glass, and mountings constructed from [[plywood]], [[Teflon]] strips and other low-cost materials.<ref name="levy">{{cite journal |authorlink=David H. Levy |title=Walden of the Sky |journal=[[Sky & Telescope]] |pages=84–87 |date=September 1995|bibcode=1995S&T....90c..84L |last1=Levy |first1=David |last2=Aguirre |first2=E. |volume=90 |issue=3 }}</ref> Since he built these telescopes as aids in his [[avocation]] of instructional [[sidewalk astronomy]], he preferred to call the design a "sidewalk telescope".<ref>{{cite book |url=https://books.google.com/books?id=qnN_KRFgITQC&dq=dobsonian+dobson&pg=PA17 |author=Fred Watson |title=Why is Uranus Upside Down? |date=October 2007 |publisher=Inc NetLibrary |page=17|isbn=9781741762761 }}</ref> Dobson combined all these innovations in a design focused towards one goal: building a very large, inexpensive, easy to use, portable<ref>{{cite book |url=https://books.google.com/books?id=liOMrb227N8C&dq=dobsonian&pg=PA25 |author=Knoll, Peter |title=Induced Seismic Events |date=30 July 1996 |page=25|publisher=Springer |isbn=9783764354541 }}</ref> telescope, one that could bring [[Deep-sky object#Observations and activities|deep-sky]] astronomy to the masses.<ref>{{cite book |url=https://books.google.com/books?id=I7qnSOAVa90C&dq=dobsonian&pg=PA92 |author=Albert, David H. |title=And the Skylark Sings with Me  |date=January 1999 |page=93|publisher=New Society Publishers |isbn=9780865714014 }}</ref>

===Dobson's design innovations===
[[File:Two dobsonians.jpg|thumb|right|Two [[Amateur telescope making|Amateur]] built Dobsonians at [[Stellafane]] in the early 1980s]]
Dobson's design allows a builder with minimal skills to make a very large telescope out of common items. Dobson optimized the design for observation of faint objects such as [[star cluster]]s, [[nebula]]e, and [[galaxies]] (what amateur astronomers call ''[[deep sky object]]''s). These dim objects require a large objective mirror able to gather a large amount of light.  Because "''deep sky''" observing often requires travel to [[Dark-sky movement|dark locations]] away from city lights, the design benefits from being more compact, portable, and rugged than standard large Newtonian telescopes of times past, which typically utilized massive [[Equatorial mount#German equatorial mount|German equatorial mounts]]. John Dobson's telescopes combined several innovations to meet these criteria, including:

* '''Nontraditional [[altazimuth mount|alt-azimuth]] mount''': Instead of a standard mount using axial bearings, Dobson opted for a very stable design that was simple to build, and which had fewer mechanical limitations when used with large and heavy telescopes. He modified the classical fork mount into a free-standing three-piece construction, which holds the telescope steady on seven discrete support points and allows for easy and safe repositioning of a large and heavy telescope.
** The classical Dobsonian mount (refer to Fig.1) consists of a flat horizontal "ground board" platform (Fig.1, black) on top of which are attached three of the seven supports (Fig.1, bottom yellow). Upon these three supports rests a box construction called a "rocker box" (Fig.1, dark blue). A loose center-bolt (Fig.1, dark green) keeps the rocker box centered and allows it to pivot above the ground board. On opposing sides of the rocker box, semicircular depressions are cut out from the top edge of each wall (the rocker box is open on the top and on the back). Each depression has a widely spaced pair of supports installed in the cut (Fig.1, top yellow). The telescope optical tube assembly (OTA, Fig.1, light blue) has two large round [[trunnions]] (or arc-shaped rails for larger telescopes) secured on the left and right sides (Fig.1, red). Their common axis intersects the [[center of gravity]] of the telescope OTA. The trunnions (commonly known as altitude bearings) rest atop the aforementioned four supports in the top cutouts of the rocker box. To raise the telescope (altitude), just lift the tube and the trunnions will slide over the four supports. To move the telescope left or right (azimuth), push or pull the top rim of the OTA (some have a dedicated handle) so that the pivoting rocker box slides over the ground board's three supports. [[File:Dob.png|thumb|right|Fig.1 Dobsonian mount schematics]]
** Classical Dobsonian mount parts are typically made from plywood and other cheap materials which are glued, screwed, or even nailed together. In contrast to other telescope mount types, no precision-machined mechanical parts are required. For smooth sliding motions, small [[Teflon]] (PTFE) blocks are used for the seven supports. Their surface sizes can be precisely calculated for the particular OTA weight. To improve the smoothness and steady position-holding, the bottom of the rocker box is typically covered with micro-textured [[Formica (plastic)|Formica]]. The altitude trunnions often have a large diameter, and can also be covered with textured material. For larger telescopes, semicircular wood pieces or arc-shaped rails can be used instead of round trunnions.
** The use of Teflon over textured material combines with gravity-produced wedging forces to create a unique smooth action, transitioning from rock steady to smooth motion and back. Thus a clamp mechanism is not needed to prevent unintentional motion of the telescope, unlike most other telescope mounts. The steadiness of the classical Dobsonian is unparalleled, as the telescope is actually not rotating on two axes as other mounts but instead statically standing on seven solid blocks (until pushed to a new position). 

* '''Thin mirrors''': Instead of costly [[Pyrex]] mirror blanks with the standard 1:6 thickness ratios<ref name="books.google.com"/> (1&nbsp;cm thick for every 6&nbsp;cm in diameter) so they don't flex and sag out of shape under their own weight, Dobson used mirrors made out of glass from surplus ship porthole covers usually with 1:16 thickness ratios.<ref>{{cite book |url=https://books.google.com/books?id=l2TNnHkdDpkC&dq=dobsonian+amateur+telescope+makers&pg=PA286 |author1=Newton, Jack |author2=Teece, Philip |title=The Guide to Amateur Astronomy |date=19 January 1995 |page=288|publisher=Cambridge University Press |isbn=9780521444927 }}</ref> Since the telescope design has an alt-azimuth mount, the mirror only has to be supported in a simple cell with a backing of indoor/outdoor carpet to evenly support the weight of the much thinner mirror.

* '''Construction tubes''': Dobson replaced the traditional aluminum or fiberglass telescope tube with the thick compressed paper tubes used in construction to pour concrete columns. "Sonotubes", the leading brand employed by Dobson, are less expensive than commercially available telescope tubes and are available in a wide variety of sizes. For protection against moisture, the tubes were usually painted or coated with plastic. Sonotubes are claimed{{fact|date=March 2025}} to be more rugged than aluminum or fiberglass tubes which can dent or shatter from impacts during transport. They have the added advantage of being thermally stable and non-conductive, which minimizes unwanted convection currents in the light path caused by handling of the tube assembly. 

* '''A square "mirrorbox"''': Dobson often used a plywood box for the tube base and mirror housing, into which the tube was inserted. This gave a rigid flat surface to attach the mirror supports, and made it easy to attach the trunnions.

==Characteristics==
The Dobsonian design has the following characteristics:
*'''Altazimuth mount''': An [[Equatorial mount|equatorial telescope mount]] with clock drive was left out of the design. Equatorial mounts tend to be massive (less portable), expensive, complicated, and have the characteristics of putting the eyepiece of Newtonian telescopes in very hard to access positions.<ref>{{cite book |url=https://books.google.com/books?id=liOMrb227N8C&dq=dobsonian&pg=PA25 |author=Knoll, Peter |title=Induced Seismic Events |date=30 July 1996 |page=25 |publisher=Springer |isbn=9783764354541 |quote=Dobson ... promoting causal visual observing}}</ref> Altazimuth mounts cut the size, weight and cost of the total telescope and keep the eyepiece in a relatively easy to access position on the side of the telescope. The altazimuth mount design used in Dobsonian designs also adds to simplicity and portability; there is no added mass or need to transport counter weights, drive components, or tripods/pedestals. Setting up for hard tube dobs simply involves placing the mount on the ground, and setting the tube on top of it. The weight of the Dobsonian style altazimuth mount is distributed over large simple bearing surfaces so the telescope can move smoothly under finger pressure with minimal backlash.
 
:The altazimuth mount does have its own limitations. Un-driven altazimuth mounted telescopes need to be "nudged" every few minutes along both axes to compensate for the rotation of the Earth to keep an object in view (as opposed to one axis for un-driven equatorial mounts), an exercise that becomes more difficult with higher magnifications.<ref>{{cite book|last=Grego|first=Peter|title=Moon Observer's Guide|url=https://archive.org/details/fireflymoonobser00greg|url-access=registration|year=2004|publisher=Firefly Books|isbn=978-1-55297-888-7|page=[https://archive.org/details/fireflymoonobser00greg/page/60 60]}}</ref> The altazimuth mount does not allow the use of conventional [[setting circles]] to help in aiming the telescope at the coordinates of known objects. They are known for being difficult to point at objects near the [[zenith]], mainly because a large movement of the azimuth axis is needed to move the telescope pointing by even a small amount. Altazimuth mounts are also not well suited for [[astrophotography]].

*'''Large objective diameter compared to mass/cost'''
**''Low mass to objective size ratio'': The Dobsonian design's structure as measured in volume and weight is relatively minimal for any given objective diameter when compared to other designs.<ref group=lower-alpha>This ratio ensures that per inch of objective diameter, a Dobsonian will weigh less and require less space than other types and is thus the most portable design.</ref>
**''Low cost to objective size ratio'': From a cost perspective, a user typically gets more objective diameter per unit of cost with the Dobsonian design.<ref>{{cite web |url=http://www.seqas.org/Documents/Begin.pdf |publisher=South East Queensland Astronomical Society Inc. |title=Recommendations for Beginning Amateur Astronomers, page&nbsp;4 |access-date=2009-02-25 |archive-date=2006-08-19 |archive-url=https://web.archive.org/web/20060819082545/http://www.seqas.org/Documents/Begin.pdf |url-status=dead }}</ref>
*'''Good "Deep Sky" telescope''': The Dobsonian design of maximized objective diameter combined with portability makes the design ideal for observing dim star clusters, nebulae, and galaxies (deep sky objects), an activity that requires large objectives and travel to dark sky locations. Since these objects are relatively large, they are observed at low magnifications that do not require a clock-driven mount.
*'''Balance Issues''': Designs that have the telescope tube fixed in relationship to its altitude bearings can be put out of balance by the addition or subtraction of equipment such as cameras, [[finderscope]]s or even unusually heavy [[eyepiece]]s. Most Dobsonian telescopes have enough friction in the bearings to resist a moderate amount of imbalance; however, this friction can also make it difficult to position the telescope accurately. To correct such imbalance, counterweights are sometimes hooked or bolted onto the back of the mirror box.

== 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.

==Commercial adaptations==
[[File:Dobson-mount.jpg|thumb|upright|Commercially mass-produced 10" Dobsonian]]
[[File:Teeter 16 inch telescope.jpeg|thumb|upright|Commercially custom-built 16" truss Dobsonian]]

The original intent of the Dobsonian design was to provide an affordable, simple, and rugged large-aperture instrument at low cost.<ref name="howandwhy_p61-62">{{cite book |last=Dobson |first=John L. |authorlink=John Dobson (amateur astronomer) |title=How and Why to Make a User-Friendly Sidewalk Telescope |publisher=Everything in the Universe |editor=Sperling, Norman |year=1991 |pages=61–62 |isbn=0-913399-63-9}} – 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.</ref> These same attributes facilitate their mass production. One of the first companies to offer Dobsonian telescopes commercially was the now defunct company Coulter Optical (now part of Murnaghan Instruments). In the 1980s, they helped popularize the design with "Odyssey" models of various sizes, with tubes made of Sonotube and following Dobson's original concept of simplicity.<ref name="Know Thy Dob">{{cite book |last=English|first=Neil |title=Know Thy Dob: Choosing and Using a Dobsonian Telescope|publisher=Springer |year=2011 |isbn=978-1-4419-8785-3}}</ref><ref>{{cite web |url=https://sites.google.com/site/coulterodyssey/index |title=The Odyssey 8 Site |access-date=2020-06-22 |archive-date=2021-11-16 |archive-url=https://web.archive.org/web/20211116170338/https://sites.google.com/site/coulterodyssey/index |url-status=dead }}</ref>
By the 1990s, [[Meade Instruments]], [[Orion Telescopes]] and other manufacturers began to introduce upgraded Dobsonian models. These imported mass-produced scopes included such niceties as metal tubes and more refined hardware, and are still very affordable.<ref name="Know Thy Dob" />

Since the 1990s, manufactured Dobsonians using the truss tube design have become increasingly popular. The first commercial truss Dobsonian was released into the market by [[Obsession Telescopes]] in 1989.<ref>{{cite web |url=https://www.manta.com/c/mm0f33j/obsession-telescopes |title=Obsession Telescopes}}</ref> Later American manufacturers included StarStructure,<ref>{{cite magazine |last=Nelson |first=Anthony |date=May 2005 |title=The Big Easy |url=https://astronomy.com/-/media/import/files/pdf/7/c/1/0505_starstructure_dobsonian.pdf |magazine=Astronomy Magazine |access-date=2020-06-22 |archive-date=2022-01-02 |archive-url=https://web.archive.org/web/20220102210422/https://astronomy.com/-/media/import/files/pdf/7/c/1/0505_starstructure_dobsonian.pdf |url-status=dead }}</ref> Webster Telescopes,<ref>{{cite web |url=https://astromart.com/reviews-and-articles/reviews/telescopes/newts/show/webster-telescopes-d18 |title=Webster Telescopes D18 |last=Bonandrini |first=Dave |date=8 Aug 2009 }}</ref> AstroSystems,<ref>{{cite web |url=https://www.cloudynights.com/articles/cat/mi/astrosystems-telekit-r1837 |title=Astrosystems Telekit |last=Shinn|first=Brett |date=16 Dec 2008 }}</ref> Teeter's Telescopes,<ref>{{cite web |url=https://skyandtelescope.org/astronomy-equipment/teeters-telescopes-custom-dobsonian/ |title=Teeter's Telescopes Custom Dobsonian |publisher=Sky & Telescope |date=18 Jan 2016 }}</ref> Hubble Optics,<ref>{{cite web |url=https://astronomytechnologytoday.com/2019/06/02/review-of-hubble-optics-ul16-dobsonian-telescope/ |title=Review of Hubble Optics UL16 Dobsonian Telescope |last=Parkerson |first=Stuart |publisher=Astronomy Technology Today |date=2 Jun 2019 }}</ref> Waite Research,<ref>{{cite web |last=Harrington |first=Phil |date=27 Jul 2015 |title=Waite Research Renegade 20 |url=https://www2.astronomy.com/-/media/Files/PDF/Equipment%20reviews/2015/0915_StarProducts.pdf |archive-url= |archive-date= |website= |publisher=Astronomy Magazine}}</ref> and New Moon Telescopes.<ref>{{cite web |url=http://www.cnyo.org/wp-content/uploads/2013/06/2013june22_ATT_NMT_CNYO_article.pdf |title=16-inch f/4.5 collapsible-truss Dobsonian from New Moon Telescopes |last=Allis |first=Damian G. |publisher=Astronomy Technology Today |date=May 2013 }}</ref> These low-volume builders offer premium objective mirrors, high-end materials and custom craftmanship, as well as optional computer controlled [[GoTo (telescopes)|GoTo]] systems. Some also produce "ultra-light" models that offer greater portability.<ref>{{cite web |url=https://astronomy.com/observing/product-reviews/2009/05/obsession-18-inch-uc-telescope |title=Obsession 18-inch UC telescope |last=Shibley|first=John |publisher=Astronomy Magazine |date=19 May 2009 }}</ref>

In the 21st century, truss Dobsonian models are also mass-produced by Meade, Orion, [[Explore Scientific]] and others. Mostly manufactured in China, they offer good quality and value while being considerably less expensive than the premium scopes described above.<ref name="Know Thy Dob" /> In 2017, [[Sky-Watcher]] introduced its line of large Stargate models.<ref>{{cite web |url=https://skyandtelescope.org/astronomy-equipment/new-products/sky-watchers-stargate-truss-tube-dobsonian-telescopes/ |title=Sky-Watcher's Stargate Truss-Tube Dobsonian Telescopes|publisher=Sky & Telescope |date=30 Oct 2017}}</ref>

Solid tube commercial Dobsonians typically have a maximum aperture of 12 inches (305 mm) due to the size of the tube. Truss Dobsonians of 12 to 18 inches (305 to 457 mm) are the most popular sizes, as they offer substantial aperture yet can still be easily set up by one person. Several manufacturers offer models of 24 inch (610 mm) aperture and greater. Truss Dobsonians are the largest telescopes commercially available today. A massive 36 inch (914 mm) aperture Hybrid model from New Moon Telescopes was displayed at the 2018 Northeast Astronomy Forum.<ref>{{cite web |url=https://skyandtelescope.org/astronomy-news/northeast-astronomy-forum-2018/ |title=News & Views from the 2018 Northeast Astronomy Forum|publisher=Sky & Telescope |date=23 Apr 2018}}</ref> In 2019, a huge 50 inch (1270 mm) aperture folded Newtonian from Canadian based Optiques Fullum was installed in New Jersey.<ref>{{cite web |url=https://astronomytechnologytoday.com/2019/07/02/newtonian-telescope/ |title=Huge 50" Newtonian Telescope Installed in New Jersey |last=Parkerson |first=Stuart |publisher=Astronomy Technology Today |date=2 Jul 2019 }}</ref>

==The Dobsonian's effect on amateur astronomy==
The Dobsonian design is considered revolutionary due to the sheer size of telescopes it made available to amateur astronomers.<ref>
{{cite book
 |author=Hitt, Jack
 |year=2012
 |title=Bunch of Amateurs: A search for the American character
 |publisher=Crown/Archetype
 |pages=231–234
}}
</ref><ref>
{{cite book
 |author=Cooke, Antony
 |year=2006
 |title=Visual Astronomy Under Dark Skies: A new approach to observing deep space
 |publisher=Springer Science & Business Media
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</ref><ref>
{{cite book
 |author=English, Neil
 |year=2012
 |title=Classic Telescopes: A guide to collecting, restoring, and using telescopes of yesteryear
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|bibcode=2013ctgc.book.....E
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</ref> The inherent simplicity and large aperture of the design began to attract interest through the 1970s since it offered the advantage of inexpensive large instruments that could be carried to dark sky locations and [[star party|star parties]] in the back of a small car and set up in minutes.

The result has been a proliferation of larger telescopes which would have been expensive to build or buy, and unwieldy to operate, using "traditional" construction methods. Whereas an 8&nbsp;inch Newtonian telescope would have been considered large in the 1970s, today 16&nbsp;inch systems are common, and huge 32&nbsp;inch systems not all that rare.<ref>
{{cite book
 |author=Mullaney, James
 |year=2009
 |title=A Buyer's and User's Guide to Astronomical Telescopes and Binoculars
 |edition=1 |page=38
}}
</ref>

In combination with other improvements in observing equipment, such as [[Dichroic filter|narrow-pass optical filter]]s, improved [[eyepiece]]s, and digital [[digital photography|visible]] and [[infrared photography#Digital cameras|infrared]] photography, the large apertures of the Dobsonian have dramatically increased the number of objects observed as well as the amount of detail in each object observed. Whereas the amateur astronomer of the 1970s and 1980s typically did not explore much beyond the Messier and brighter [[New General Catalogue|NGC]] objects, thanks in part to Dobsonians, modern amateur astronomers routinely observe dim objects listed in obscure catalogues, such as the [[Index Catalogue|IC]], [[Abell catalogue|Abell]], [[Kohoutek]], [[Rudolph Minkowski|Minkowski]], and others once considered reference works only for professional astronomers.

When mounted on an [[equatorial platform]] the difficulties using a Dobsonian for short-exposure (≲&nbsp;1&nbsp;hr) [[astrophotography]] are obviated. This has opened up the field of high precision asteroid [[astrometry]] (and discovery) to the amateur wishing to contribute minor planet positions to the [[Minor Planet Center]]. It also makes possible searches for new, faint objects such as [[novae]] / [[supernovae]] in local galaxies, and [[comet]]s (for reports to the [[Central Bureau for Astronomical Telegrams]]).

==See also==
* [[List of telescope types]]

==Notes==
{{notelist}}

==References==
{{reflist}}

* [http://www.smithsonianmag.com/science-nature/35-who-made-a-difference-john-dobson-113799923/ Moser, Don (November 1, 2005) ''35 Who Made a Difference: John Dobson'' – Smithsonianmag.com]
* [http://www.accessmylibrary.com/coms2/summary_0286-5453802_ITM/abstract Moser, Don (April 1989) "''A Salesman for the Heavens Wants to Rope You In''", Smithsonian Magazine.]
* {{cite book|first=Martin|last=Mobberley|title=The New Amateur Astronomer|url=https://books.google.com/books?id=woJKq6o1zAMC&pg=PT32|year=2004|publisher=Springer Science & Business Media|isbn=978-1-85233-663-9|page=21}}
* {{cite book|first=David H.|last=Albert|title=And the Skylark Sings with Me: Adventures in Homeschooling and Community-based Education|url=https://archive.org/details/andskylarksingsw0000albe|url-access=registration|year=1999|publisher=New Society Publishers|isbn=978-0-86571-401-4|page=[https://archive.org/details/andskylarksingsw0000albe/page/92 92]}}
* {{cite dictionary |url=https://books.google.com/books?id=kX_DAEsOWssC&dq=dobsonian&pg=PA60 |article=Dobsonian |author=Woodruff, John |title=Firefly Astronomy Dictionary |year=2003 |page=60|publisher=Firefly Books |isbn=9781552978375 }}
* {{cite book|first=Timothy|last=Ferris|title=Seeing in the Dark: How Amateur Astronomers Are Discovering the Wonders of the Universe|url=https://books.google.com/books?id=9gUjaCMlX5oC&pg=PA37|year=2003|publisher=Simon and Schuster|isbn=978-0-684-86580-5|page=37}}
* {{cite book |author1=Kriege, David |author2=Berry, Richard |title=The Dobsonian Telescope: A practical manual for building large aperture telescopes |year=1997 |publisher=Willmann-Bell |isbn=0-943396-55-7}}

==External links==
{{commons category|Dobsonian telescopes}}
*[http://sidewalkastronomers.us/ Sidewalk Astronomers Organization]
* San Francisco Sidewalk Astronomers' [http://www.sfsidewalkastronomers.org/index.php?page=building-telescopes telescope building page]
*[http://www.raycash.org/cdobplans.htm Complete Plans for Building a Dobsonian Telescope]
*[http://www.cruxis.com/scope/scope1070.htm The Largest Portable Dobsonian Telescope in the World (42 inch - 107&nbsp;cm)]
*[https://blog.nationalgeographic.org/2013/11/08/worlds-largest-backyard-telescope/ World's Largest Backyard Telescope]

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[[nl:Montering (telescoop)#Dobsonmontering]]