Dobsonian vs Newtonian – What’s the Difference?

Figuring out what type of telescope you want is the first step in getting yourself a new telescope. There are a wide variety of names for the various differentiations of telescope, and if you’re new to astronomy then it can be a little overwhelming. Two of the most popular telescope names that you might have heard of are Dobsonian and Newtonian, which many people think are two different types of telescope completely. They’re incorrect!

These technical terms can be difficult to come to terms with, so it’s important you do a little research beforehand. Otherwise, you may end up purchasing a telescope that isn’t really the best for your circumstance. So, lets have a closer look at these different types of telescopes that you should be aware of.

Dobsonian vs Newtonian

The answer is that Dobsonian and a Newtonian can actually be the same thing. A Newtonian refers to the telescope optics, whereas a Dobsonian refers to Newtonian telescope with some specific features like an altazimuth mount and often thin mirrors.

A telescope can be a Newtonian and also a Dobsonian at the same time. As you probably expect, Newtonians date all the way back to the 1600s to the founder of this type of telescope, Sir Isaac Newton. Dobsonians have only been around since the 1960s, but have grown very quickly in terms of popularity.

So, we’ve established that it is generally difficult to compare these two terms because one encompasses the other. But, we can have a look at the two in a closer fashion to help you know what each specific one really is.

Newtonian Telescopes

As you might have guessed, the Newtonian telescope is named after it’s inventor Issac Newton – yep, the same guy that discovered gravity and is considered as one of the most important scientists of all time. Back in 1668 when it was invented, it became the first known version of the reflecting telescope.

Simply described, a reflecting telescope is a telescope that uses a mirror to collect and focus light to produce an image. Sometimes, light will transfer through a surface easily when it hits something transparent (like glass). But when light hits a surface that it can’t get through (like a mirror) then it bounces off the surface predictably. This light then produces an image through the eyepiece of the telescope.

Generally, a Newtonian telescope is much easier to build than other forms of reflecting telescope, like a Cassegrain. To describe a Newtonian telescope simply, light enters into the telescope and hits the primary, curved mirror at the alternative end from entry. This then rebounds onto a smaller, secondary mirror which reflects the image through the eyepiece. This is a simple explanation, but it is easy to understand.

Dobsonian Mount/Telescopes

Many people refer to a Dobsonian as the type of optics in the telescope, but where the Dobsonian different to other telescopes is really the mount that is used for the telescope, not the optics. One common question is whether a Dobsonian is always going to used Newtonian telescope optics – the answer is that 99% of the time, yes. This is due to the placement of the eyepiece, which is ideally suited for a Dobsonian telescope, though there are cases of Cassegrain reflectors being used for this too.

The Dobsonian was only created in the mid 1960’s by astronomer John Dobson. He was often referred to as the ‘Star Monk’ due to the large portion of his life he lived with a monastery – he led an interesting and varied life, that’s for sure! Dobson is widely credited as helping increase the popularity of astronomy within the everyday man, as his amateur astronomy club in San Francisco became increasingly popular – this is where he created the Dobsonian telescope.

The Dobsonian has become so popular nowadays primarily for the main reason that it is very effective, yet available at a cheap price – great if you want to purchase a budget telescope. Although Dobson himself says that the design is so simplistic because he didn’t have the knowledge to make a more technical telescope mount, this seems to have worked out in his favour.

Generally, Dobsonian telescopes are made to see deep sky objects like planets and galaxies. This is due to a few reasons – primarily because the Dobsonian, which used Newtonian optics, allows a large amount of light into the telescope. This allows us to see images further in the distance, which requires a lot of light to be able to do this.

It’s necessary to be in an area with low light pollution to be able to view these kinds of objects, so you’ll want to avoid heavy polluted city centres. Dobsonian telescopes have a short focal length, which means that they are relatively short and extremely portable – another reason why they are particularly popular amongst amateur astronomers.

What makes a Dobsonian?

As I’ve stated, a Dobsonian is a Newtonian, but there are some specific things which make it different than a Newtonian telescope. Here are some of the thing you’ll want to know which made a Dobsonian telescope what it is when Dobson introduced some cheaper variations on a standard telescope.

• Altazimuth mount – A Dobsonian isn’t a Dobsonian without an altazimuth mount. It’s one of the simplest mounts there is, and the likelihood is that you’ve seen one without even knowing it. It’s the most popular telescope mount nowadays, along with equatorial mounts. Both of these mounts are generally considered the most suitable, because they’re easy to rotate at all angles.
• Tubes – In a regular telescope, the material that was generally used for tubes was always aluminium or fiberglass. When Dobson created his telescope, he replaced these tubes with paper tubes – not soft paper, but hard paper that you’d generally find on construction sites. This makes the Dobsonian more robust, and better for carrying around without worry of damaging your telescope. Dobsonian tubes are twice the length of some standard Newtonians, as a Dob uses a flat secondary mirror as opposed to curved.
• Mirrors – Another of the main things that makes a Dobsonian what it is is the thin mirrors that it used. Whilst typically in the past thicker, Pyrex mirrors were used, much thinner and cheaper mirrors were used with the Dobsonian. The way that the mount is designed allowed a thinner mirror.

These are the main differences that Dobson introduced as opposed to a Newtonian or regular reflecting telescope. Although these differences may not seem like much, they really have made a massive difference in bringing astronomy into the mainstream and making it more affordable for amateurs.

Conclusion

If you’re a beginner, then you’ll undoubtedly want to look at getting yourself a Dobsonian telescope before anything else. Generally, due to their cheap price and portability they make a much better option than other types of telescopes, like refracting telescopes. They are perfect for amateurs who are just getting started and don’t need anything particularly expensive.

There are an abundance of different Dobsonian telescopes available on the market currently, and it depends on what you need to find the one that works well for you. The most notable variation of reflecting Newtonian telescope is the Dobsonian, and this is usually the best place to start for a beginner or intermediate.

Hopefully, this has cleared up any confusion that you may have about the difference between a Dobsonian and a Newtonian telescope. It’s common to see people thinking they are entirely different things, whereas really a Dobsonian is just the most popular variation of a Newtonian telescope.