How does a Dobsonian Telescope Work?

How does a dobsonian telescope work

Planetary viewing is quite possibly the first thing that people do when starting off their adventure into amateur astronomy. It is very easy with the right equipment and it’s totally cool to have a serious telescope all set up and configured to explore clear images of Saturn’s rings.

As we all know, the most resourceful telescope is the one that’s used regularly, not the one that lives in a box. It needs to be user-friendly, practical, and enjoyable to work with. Therefore, figuring out what type of telescope you want is the key to getting yourself a worthy telescope.

Dobsonian is one of the most popular telescope labels you’ll come across in the field of astronomy. The Dobsonian telescopes are often associated with excellent simplicity, which makes them incredibly functional and great for professionals and amateur astronomers alike.

It’s a simple set of optics on a simple altazimuth platform.

However, we can’t afford to give a blind eye to other features that make Dobs a standout. From larger aperture to portability and ease of use, there is more to Dobsonians than meets the eye.

So, in this article, we will have a closer look at Dobsonian telescopes, see what they are, how they work, and what makes them so good.

Dobsonian Telescope Origin

The Dobsonian is a type of reflecting telescope that was first developed by a Hindu Vedanta monk known as John Dobson in the 1960s in San Francisco. Although he had a degree in chemistry, Dobson had always been interested in spiritual studies and cosmology

In an attempt to experience fundamental reality, Dobson became inquisitive about the nature of the universe and how he could coordinate it with Hindu teaching.

However, during this time, even a simple 6-inch Newtonian of the traditional form was way beyond reach for Dobson as these instruments were made with costly special components and were mostly not even portable.

The high-quality eyepieces, heavy-duty equatorial mounts, and thick Pyrex mirror blanks were far out of reach for the Hindu Vedanta monk.

Although a fairly dreamy monk, Dobson was certainly no ordinary man. He came up with a great idea of creating his own telescope- something that could help people explore the universe. The outcome of this endeavor was a telescope that currently carries his name.

Dobsonian Telescope Design Concepts

Dobsonian Telescope Design Concepts

The first designs of Dobson telescopes featured porthole glass for the main mirrors, sanded surfaces, and cultured with parts created from roofing materials and jeweler’s blusher. And the tubes were cardboard and the eyepieces were scavenged from war surplus binoculars.

These telescopes were silvered with nitrate compounds developed from fertilizer. Completed telescopes also had enhanced mirrors with slings developed from seat belts, and the whole thing swiveled up and down just like a cannon.

Modern Dobsonian models are quite exceptional. The stated portholes have particularly been swapped with optical glass.

Instead of cardboard, the tubes are now metal with thin metals and sometimes made out of aluminum frames. Larger mirrors still have splints/slings, but they are mostly steel and Kevlar cables.

Dobsonian telescopes are known to be particularly simple and inexpensive to manufacture, although imported models from abroad are often an easy choice for the majority of people.

So, How Does a Dobsonian Telescope Work?

So, How Does a Dobsonian Telescope Work

As earlier mentioned, the Dobsonian telescope falls in the category of reflecting telescopes, which essentially use a primary mirror and secondary mirror instead of lenses.

They are much of an adaptation to the renowned Newtonian reflector, where light is focused by a concave primary mirror and the image bounces off a small flat diagonal mirror to the side of the tube.

The concave parabolic mirror- which is intended to capture light rays from different celestial bodies- is fixed on the lower part of the telescope while the eyepiece is set on the side of the telescope tube, up near the front.

In other words, when a Dobsonian telescope is pointed at a celestial target, it collects light rays from that object through the opening (aperture). This light travels inside the scope’s optical tube and hits the primary mirror fixed at the end of the telescope tube.

The light incident on the collecting mirror (the curved primary mirror) is then deflected towards the flat secondary mirror, where it is directed further towards the focuser where the eyepiece is placed. The image focusing and magnification take place within the eyepiece.

With a Dobsonian telescope, the eyepiece is set orthogonally to the focuser in the tube. This causes the final image to appear overturned, but since the space has no up/down, it’s really not much of a big deal.

Dobsonian telescope Set Up

Dobsonian telescope Set Up

For best performance, the telescope must be properly collimated. This refers to the proper alignment of the primary mirrors such that the lighting bouncing or deflecting off it is seamlessly directed toward the flat secondary mirror without any distortion or loss of light rays.

Some widely-produced Dobsonian telescopes feature stunted bearings that require extra tension with locks or springs so they do not shift when changing accessories on the front part of the instrument.

While some come with bearings that can slide across the tube, the best Dobsonian models feature vast altitude bearings that are not basically not garbled by the center of gravity.

Another thing worth mentioning is that most Dobsonian telescopes are entirely manual. That means the viewer will have to find targets using star charts or smartphones and then unhurriedly work the scope to track the sky.

The Dobsonian is a very simple scope overall. In fact, they are dubbed “light buckets” due to the generous opening that makes their light-gathering leverage one of the best on the market.

Provided you are ready to manually find and track your celestial targets, a Dobsonian telescope is certainly your best bet for planetary viewing.

As for accessories, experts suggest that you experiment with eyepiece and Barlow lenses to see what works best subject to what you observe.

Dobsonian Telescope Mirrors

Dobsonian Telescope Mirrors

The fact that Dobsonian telescopes follow the Newtonian design means that they have the same type of mirrors as the Newtonian reflector. These telescopes have an open end where the light enters the scope.

The primary mirrors or the collective mirrors are fixed at the bottom of the telescope and are designed to gather all the light that has entered the tube.

When the viewer looks through the eyepiece on the side, the telescope eyepiece targets the secondary mirror. The size of the telescope is largely influenced by the size of the mirrors.

For instance, a 12-inch Dobsonian telescope basically describes the measurement of the concave primary mirror at the lower part of the tube.

The size of the mirror is directly proportional to the length of the tube. Large Dobsonian telescopes will have larger mirrors to allow more light to enter the tube.

Dobsonian mirrors will need to be collimated. Collimation is the process where the primary mirror and secondary mirrors are aligned with each other so there are no warped images.

This is especially the case when the instrument is coming straight from the manufacturer. Although they only need slight adjustments, you can do this using various tools such as a laser collimator to help in the process.

Dobsonian Telescope Mount

Dobsonian Telescope Mount

Dobsonian telescopes are mounted on a simple alt azimuth mount. This mount holds the tube much like a cannon, as it swivels up and down and right and left.

To project your optical tube assemblies towards a select target in the sky, the viewer will first need to manually direct the telescope to the left or right by slowly pushing the azimuth turntable.

The altitude axis might as well need some adjustment. You can do this by turning the control knob on the side of the rocker box so that you are able to swivel the optical tube up and down.

After getting the desired object at the center of the eyepiece, you can now fasten the control knob so that the tube remains in place.

The best thing about this mount is that it has very basic construction, usually wooden, but incredibly stable and easy to set up. They are usually robust, which is particularly important when working with large aperture telescopes.

This makes it far better and cheaper than other mounts in the same class. In fact, the altazimuth mount is the central part distinguishing a Dobsonian scope from a Newtonian telescope.

When setting up the Dobsonian mount, make sure the base of your observing spot is properly leveled on the ground. Some experts also suggest placing the mount on a vibration pad which significantly eases vibrations around the instrument for a better viewing experience.

Having said that, now let’s get closer to what makes Dobsonian reflecting telescopes so popular.

Large Aperture

Large Aperture

One of the major benefits of Dobsonian telescopes is that they’re recognized for offering the widest aperture at the lowest price.

Aperture refers to the size of the opening of the scope. This is where the light enters the optical tube assembly. The larger the aperture, the more light incident the telescope will collect and the brighter and sharper the image will be.

This makes them a popular choice for visual astronomy: the moon, the planets, as well as deep-sky objects as they have a large objective diameter compared to other designs.

An equatorial telescope mount 8 inches costs relatively twice that of an 8-inch Dobsonian. An 8-inch Schmidt-Cassegrain is three (sometimes four) while an 8-inch refractor telescope costs about as much as a decent automobile.

For this reason, someone looking for a decent-sized, low-cost telescope will be wise to consider a Dobsonian.  These reflecting telescopes are generally ideal for large openings- six inches up to 36 inches- mainly because they use mirrors rather than glass.

Again, this makes them cheaper to manufacture in comparison to refracting telescopes.

Portability and Ease of Use

Portability and Ease of Use

Dobsonians are renowned as some of the easiest and fastest telescopes to set up.

All you need to do is set them on a level observation spot, make sure the mirrors are well collimated, get your eyepiece, track your target with the help of a star chart or mobile phone, and point the scope at the target and that’s it.

Of course, an 8-inch Schmidt-Cassegrain can be fairly more compact than a Dobsonian reflector telescope, but the setup tends to be a little more complicated.

The stated altazimuth mount cuts weight, cost, and size, which, in, turn, increases the portability of the overall telescopic set-up. It also assists in keeping the eyepiece in place that’s easily accessible for the telescope’s size.

The Dobsonian mounts also make it easy to rotate the scope on both horizontal and vertical axis as needed.

Dobsonians don’t Suffer Image Distortion

Dobsonians don’t Suffer Image Distortion

To experience a sharp view in your eyepiece, all the light gathered through the opening or aperture needs to be focused at the same point and time. On that note, telescopes that use lenses to collect light often suffer from what is called chromatic aberration.

Fortunately, Dobsonians are designed to counteract such minor imbalances. The fact that these telescopes use mirrors to reflect light means that the light rays will be focused precisely at the same point and at the same time.

Besides, these models are associated with sufficient friction in their bearings for offsetting a significant amount of distortion.

On the flip side though, is also said to make these telescopes a bit harder to place accurately. Sometimes counterweights are installed or hooked into the mirror’s back to rectify the rebound caused.

Great for Planetary Observation

Great for Planetary Observation

Dobsonians are well among the most suitable telescope for planetary and deep-sky viewing with a low budget.

The generous opening/aperture allows them to gather lots of light reflecting off the celestial bodies, meaning that you may experience much clearer and brighter images within the eyepiece.

These telescopes come with a maximized objective diameter and enhanced portability that make the placement perfect for observing faint star clusters, detecting nebulae, and other deep space objects.

Lower Cost than Other Types of Telescopes

Lower Cost than Other Types of Telescopes

As we stated earlier, reflectors telescopes are less costly to manufacture than refractors or even Catadioptric telescopes. They are great for amateur astronomers because they provide a more objective diameter and greater light-gathering capability for the least amount of money.

Subject to the size of the collective mirror, a commercial Dobsonian can cost anywhere between a few hundred to around $500.

Keep in mind that fancier and complex models costing upwards of $2000 will mostly be more involving to move around and set up, less stable, and more difficult to use.

The Bottom Line

The Bottom Line

With their simple mount structure, Dobs are considered easier to set up, lightweight, and often cheaper compared to other styles of mount. Moreover, the eyepiece is made to remain in place most of the time and generally doesn’t end up in an undesirable position.

So, if all you want is to explore things; stars, planets, star clusters galaxies, nebulae, and such deep-sky objects, then the best telescope (best in terms of budget and light gathering capability) is the Dobsonian telescope.

However, if you’re planning to use your telescope for astrophotography, which means taking photos of deep-sky objects, then you might want to consider a refracting or Newtonian telescope and a motorized mount instead.

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Picture of Lisa Hayden-Matthews

Lisa Hayden-Matthews

An avid Skier, bike rider, triathlon enthusiast, amateurish beach volleyball player and nature lover who has never lost a dare! I manage the overall Editorial section for the magazine here and occasionally chip in with my own nature photographs, when required.
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