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Why are Dobsonian Telescopes a Favorite Among Amateur Astronomers?

Dobsonian Telescope

The Meade 16" LightBridge

Welcome to the scary and expensive world of buying your first, or replacing your old telescope!

I am asked all the time “What telescope should I buy” or “What telescope do I need to see X with?” Nine times out of ten, I recommend a Dobsonian Telescope.

So what is a Dobsonian telescope and why are they so good? Read on to find out why.

A Dobsonian is simplicity in itself; a simple set of optics on a simple mount. But don’t be fooled by this simplicity. Dobsonian telescopes are incredibly good and are great for amateurs and professional astronomers alike. They are also very economical compared to other telescopes.

The optical part of the telescope or OTA (Optical Tube Assembly) is the same as a Newtonian reflector telescope. It consists of a primary parabolic mirror and a flat secondary mirror in an open ended tube, with a focuser for an eyepiece set on the side. Light enters the tube, reflects off of the primary mirror at the base and is then focused onto the smaller flat secondary mirror and then finally, into an eyepiece. Simple!

Credit Skywatcher.net

The benefit of this type of optical arrangement is the telescopes light gathering ability. The more light gathered, equals more fainter objects to be seen. A light bucket!

Dobsonian/Newtonian telescopes have a big advantage over telescopes with lenses such as refractors and Cassegrain telescopes, as mirrors are a lot cheaper to make than lenses. Plus they can be a lot bigger!

Both Dobsonian and Newtonian telescopes are measured by the size of the diameter of their primary (big) mirror. Dobsonian sizes range from starter scopes of 6 inches up to 30 inches, but common sizes are 8 to 16 inches in diameter. They can be many times larger and less expensive to produce than scopes with lenses.

The second part of a Dobsonian telescope is the mount. As with the optical part the mount is just as simple, if not more so! A basic manual mount which supports the optical tube and can be manually moved by hand in the Altitude (up/down) and Azimuth (left/right) axis.

The mount is usually made from wood or metal with bearings and support for the two axis of movement. More so lately, some manufacturers have put GoTo systems with motors on some Dobsonian mounts. Personally I think it’s a bit over kill for a Dobsonian, as finding objects manually by star hopping or other manual methods helps you learn the sky better and can be fun.

Dobsonian

Resist the urge to spend lots of money on small computerized scopes that will eventually never get used, as they can be too complicated or you may not see much through them apart from the brightest objects such as the Moon. A Dobsonian is a great all-around telescope, and are available in almost all telescope stores. Some people make their own homemade Dobsonian scopes too!

Due to the nature of the Alt-Az mount, Dobsonians are not suitable for long exposure astro imaging. For that you will need an equatorial mount, which will track the stars equatorially. You may have some success with webcam imaging with some of the GoTo Mounts though.

Skywatcher 10 inch Dobsonian Credit sherwoods-photo.com

Dobsonian telescopes are designed to be simple, easy to use and gather as much light as possible. Because of this robust simplicity, they are very economical and popular with astronomers of all levels of ability. My own and most favourite telescope is my Skywatcher 10-inch Dobsonian and I will probably be using it for many more years to come, as it is difficult to beat!

The name of the Dobsonian telescope comes from its creator John Dobson, who combined the simple design of the Newtonian telescope with the Alt-Azimuth mount. He originally made simple homemade scopes from household materials and ground mirrors out of the glass of old ship portholes.

John Dobson is the grandfather of Sidewalk Astronomy and co-founder of the San Francisco Sidewalk Astronomers.

Credit cruxis.com

About 

Astronomer, writer and much much more. The best Astronomy, Space info on twitter. Making Stargazing easy, fun and enjoyable for all.
Creator of Meteorwatch, meteorwatch.org and virtualastro.org

Comments on this entry are closed.

  • J. Major March 22, 2011, 7:40 AM

    Thanks for sharing this info! A lot of people ask me this question and I’ve been unsure of what to tell them, not having a telescope myself (I know, seems odd but living in a small condo in a light-swamped city makes stargazing a tough hobby!) I have been looking at some of the computerized Cassegrains myself, due to their portability, but haven’t decided on one yet. I will definitely keep this in mind, though! After all, a telescope that doesn’t gather much light isn’t very useful.

    • Olaf March 22, 2011, 10:28 AM

      My first step was a GOTO scope, which would be handy when you are in a astronomy unfavourable country like me. This way I can watch the star pop up when the clouds move for a minute or 2.
      But when I heard the noise it made, I didn’t like it to do this at night. I don’t want people to complain that the noise makes them awake. And I also love the quite sound of the night.

  • r0blar March 22, 2011, 2:39 PM

    Now look, I found a nice portable Dobs here:

    Orion 50 Monster Dobsonian Telescope

  • RapidEye March 22, 2011, 6:44 AM

    Small nit…
    When most astronomers “THINK” of a Dob, they think Newtonian Reflector on a Dobsonian mount. But technically speaking, “Dobsonian” only refers to the mount, regardless of the OTA on it. I’ve seen Refractors and SCT’s mounted on Dobsonian mounts that were attached to the top of a pier.

    I do own a 4.5″, 10″, and even an 18″ Newt on Dob mounts and agree they are the best bang for the buck. The 10″ is a real sweet spot – lots of aperture to see tons of detail in objects but still small enough to easily handle and not too expensive. Having said that, you’ll find me at the EP of my 18″ Obsession 99 clear nights out of a 100: aperture kills =-)

  • tegwilym March 22, 2011, 8:38 AM

    I get this question all the time, usually around Christmas. I usually tell people to spend a little bit more, stay away from ‘Junk’ and direct them toward one of the dobs (about 8 inches is good to start with). Size does matter! But so does simplicity too. Don’t want a beginner fighting in the darkness trying to drift align a polar EQ mount. Just plop the dob down, and look!
    I have a 10 inch mirror at home that I need to build something around, I plan on building a Dob out of it!

  • Olaf March 22, 2011, 10:25 AM

    This article is just in time. I want to buy a Orion XT10i.
    So buy? Not buy? what? ;-)

    I know that bigger means more incoming light an easier to see not so bright objects.
    But I also read that a bigger mirror also means better resolution.

    The thing that restrict me from buying it right now is the size of my car and transportable. But I want to see nebula, and this will be in a country bad for astronomy because of the light pollution. I first was thinking about a 8 Inch but it seems that only a 10 Inch would show anything in such a light polluted area.

    I also don’t understand that a $600 Orion XT10i costs 900 Euro here. Why is it double the price for us?

    • RapidEye March 22, 2011, 10:44 AM

      Olaf: BUY – Orion has top notch customer service, good quality, and the 10″ is a really good size (see above post). The “i” gives you easy “push-to” to make finding things easier, but it won’t track. Normally, that isn’t an issue, just making sure you know. You can find cheaper 10″ scopes, but not with the integrated Object Locator.

      There is a good forum on Yahoo Groups for Skyquest telescopes (i is a base on Skyquest) and you’ll find tons of good info on buying, setting up, troubleshooting, and how to get the most out of that scope.

      • Olaf March 22, 2011, 11:12 AM

        I already told my GF. I always tend to look at the big telescopes. LOL
        It is probably not going to be moved a lot, staying at my GF’s fathers place where the have some minimal All I want is to take it out, look some starts and planets and nebulas and then 30 minutes later put it back.

        The Object locator would be great to find nebula or planets even when they are behind clouds. All I have to do is point it to the correct direction that the locater is telling and wait until there is a hole in the clouds.

        The other thing is what light pollution filter would you propose to use? Are they any effective? I really want to see the Crab nebula and Orion nebula and many other galaxies out there. My previous scope only showed dots for stars, that was it. That one was 6 inch I think, basically useless. I had a small refractors and that showed me the same thing but was very portable.

        • Astrofiend March 22, 2011, 2:49 PM

          A ten incher is a nice choice, especially for the targets that you’ve listed as your primary interest. Push-to is also great – I’ve got a 12″ Meade Lightbridge and the single best upgrade I’ve made is the Argo Navis push-to scope computer. I hear the one on the Orion works nicely.

          As for LPR filters, it is all very tricky and subjective. Broadband LPR filters do a reasonable job of cutting LP. These filters cut emission from sodium, mercury and neon lamps while passing the rest, and work on a wide variety of objects including nebula & galaxies. To get the best contrast enhancement on nebula (noticably better than broadband LPR filters), you typically need to go to narrow ‘line pass’ filters, like Hbeta, [OIII], etc. These bump the contrast up heaps for the objects that they work on, but they tend to only work very effectively on a smaller number of objects, and they kill the view entirely on galaxies (galaxies are broadband emitters).

          Anyway – I recommend checking out the Lumicon website or cloudynights.com – they’ve got plenty of reviews of specific filters and whatnot.

          http://www.cloudynights.com/category.php?category_id=42&pr=2×9

          • Olaf March 23, 2011, 10:49 AM

            OK thanks.

        • RapidEye March 25, 2011, 9:22 AM

          For emmission nebula like the Crab and Orion, the best all around filter is Orion’s Ultrablock filter. Lumicons are better (I own both) but are also a lot more expensive. The Ultrablock will get you %90 of the performance at %50 of the cost.

          If money is no object, then get the Lumicon Narrowband.

          Both offer wide band filters – they are OK, but Narrow bands are better.
          Both also offer OIII filters. They will work for both the Crab and Orion, as well as a lot of others, but they are not as good of a general purpose as the Narrowband filters.

  • RapidEye March 22, 2011, 10:47 AM

    Ohhh, and Olaf – the 6″, 8″ and 10″ Orions are all the same focal length (around 1200mm) so as far as fitting them into a car, they are all about the same length. The only difference between them is the diameter, and of course, the corresponding weight. The 10″ OTA is only 35ish pounds and easily handled.

  • Lawrence B. Crowell March 22, 2011, 2:24 PM

    My next will be a Dobs as well. The big advantage is you can have a good sized telescope and the viewing can be done easily without stepping up on something. The mount is at your feet, not your waist.

    LC

  • William928 March 22, 2011, 3:20 PM

    r0blar, Nice, I want one!

  • Ryan R Scott March 22, 2011, 5:37 PM

    My first true telescope (also my first true love) was an 8-inch Dob, and I am so grateful I opted for it. I can’t describe here the number of adventures and thrills I experienced from first light. It was easy to transport and maintain, required little set up and take down time, and its star hopping qualities introduced me to many more wonders and surprises than a GOTO could ever have done – not to mention the skills I’ve learned from reading charts and understanding the lay out of our galaxy.

    I recently gave up the 8-incher, and upgraded to a new collapsible 12-inch Dob, which I’ve only had out twice in the three weeks I’ve owned it, thanks to the weather here in Toronto. So far I’ve been blown away with the views of Saturn I’ve enjoyed, and I can’t wait to get it to a dark sky site in the coming months to do some galaxy and globular cluster hunting!

    Clear skies, all!

  • santafedog March 25, 2011, 5:20 PM

    We do quite a few star tours and star parties both for industries/educational institutions and for public school outreach here in Santa Fe, New Mexico. We are asked the what kind question a lot, also, but we always preach that the person (s) should get some sky charts off the internet or get a planisphere to learn their way around the sky, then get a pair of binoculars for their first viewing. We also tell them to run screaming when they see the XMart telescope packages with 4,265 power written in large red letters on the sides. Don’t go buy a telescope before learning about what you want to see, because i see so many (usually cheeeeep) scopes at garage sales that turned out to be what i call “Hoovers” (the famous vacuum cleaner company) because they spent their life collecting dust in the garage after one or two less than pleasant attempts to see something exciting in the sky. Of course, we are always on a soap box about light pollution.

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