Dobsonian vs Cassegrain [Difference Between the Telescopes]

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If you’re interested in getting into Astronomy but are not quite sure what telescope variant is best for you and your needs, this guide will help you in your research.

While there are a lot of names, models, and brands, thankfully it is not actually as complex as it initially seems.

Understanding the different variants can ensure you make the right decision and get the right telescope for you. In order to do this, it helps to know the main differences between the different types of telescopes.

Today, I’ll be specifically looking to compare the Dobsonian and Cassegrain telescopes.

Dobsonian and Cassegrains are the two main types of Reflecting telescopes. Dobsonians are generally the better option for beginners due to their ease of use and lower cost. Cassegrain telescopes on the other hand provide the same power and performance (Aperture) yet come in a more compact design. However, the tend to be a lot more expensive.

 

In the market for a new telescope? Read my comprehensive Buyers Guide.

 

Dobsonian vs Cassegrain Telescopes

This guide will start by discussing the Dobsonian and then the Cassegrain design and then it will turn to run some comparisons between the two.

If you’re in the market for a new telescope, this will help you make a decision.

Dobsonian Telescopes

In recent years, Dobsonian telescopes have become one of the most widely used and purchased telescope variants.

Why is this?

Perhaps the standout reason is their low price in relation to their power and performance.

Being lower-priced, they serve as a great entry-level telescope and can help beginners pursue astronomy even on a limited budget, and way before they know it is something that they would like to continue long term.

If you are curious as to how they got their name, Dobsonian refers to the inventor and astronomer, John Dobson.

Now, Dobson did not outright invent them but he was the one to identify and put together all the components and elements of the design we all know today.

Before his revolutionary changes, a lot of the Reflector telescopes available on the market were too expensive for people like you and I.

Since a major overhaul of the design was to replace the most expensive parts of the telescope with cheaper, more affordable parts, Dobson has been able to transform the market and enable high-quality telescopes at a fraction of the price.

Here are some of the major distinctions of a Dobsonian telescope and what enables us to not only identify it, but distinguish it from the other Reflector Telescope designs:

Altazimuth (Alt-Az) Mount

Perhaps the standout feature of a Dobsonian is its Altazimuth (sometimes referred to as an Alt-Az) mount.

This particular type of mount is designed to be simple and easy to use. It has two perpendicular axes that enable the telescope to be easily rotated in both a vertical and horizontal plane of motion.

The mount and axes design is the most common difference that we can observe between a Dobsonian and other variants of the telescope.

Leaner Mirrors

The mirrors that are commonly used in older Reflector telescope designs are typically thicker and therefore come at a higher cost.

The Alt-Azimuth mount has enabled the Dobsonian to use leaner and thinner mirrors inside the telescope.

As this lowers the cost of manufacturing, it is in turn passed down to us and is reflected in the lower price of the Dobsonian.

Tube Frames

Another significant change implemented which has made it cheaper to construct is by using different tube frames; paper as opposed to other materials often used in Reflectors like Fiberglass and Aluminium.

Now, you may be thinking that paper is a far inferior material and will not be as strong or solid, but this is not the case.

They are more than strong enough for use in the telescope and actually help to reduce the weight of the telescope.

The Dobsonian has left a lasting impact on astronomy, and since this shift in design in the 1960s, it has enabled more people to get into astronomy who previously would not have been able to afford the equipment.

So should you always opt for a Dobsonian over other types of the telescope?

Not so fast.

One thing to mention, the way that the Dobsonian is designed means that it works best with clear skies and not so well in lower-light conditions.

So if you live in a city, or a light-polluted area, it is not going to perform as well.

Due to its optical design, it is also best used for observing Deep Space Objects (DSOs) like galaxies and distant stars.

So to confirm, a Dobsonian telescope is a type of Reflecting telescope that is widely used and can be purchased for a cheaper price than other variants.

To introduce one more term for you a Dobsonian is the cheapest style of the Newtonian telescope – named after its inventor, Isaac Newton.

If you are wondering what Newtonian Reflectors are, it is basically their optical design.

They gather and reflect it from a primary mirror onto a smaller, secondary mirror. The angle forms an image through which you can see through the eyepiece.

An alternative to Dobsonian telescopes is Cassegrain telescopes (another type of Reflecting telescope option). However, it works in a very different way to a Dobsonian.

Cassegrain Telescopes

Cassegrain Telescopes generally utilize the Reflecting telescope optical system.

However, it is important to note that some Cassegrains are classified under the category Catedioptric because they use a slightly different optical system (it is basically the combination of both Refraction and Reflecting Optical Systems).

Catadioptric telescopes are routinely considered better options because they overcome the drawbacks that come with a straight Reflecting or Refracting telescope.

To complicate things further, there are two specific types of Catedioptric Cassegrains. These are known as the Maksutov (sometimes called a Mak) and the Schmidt-Cassegrain (sometimes called a SCT).

A frequent problem with Refracting telescopes is that they can sometimes cause what is known as Chromatic Abberation (CA).

This is basically when a lens fails to focus all of the colors at the same point and is due to the reflection of light and the relative angles of the refraction mechanism.

In contrast, Reflecting telescopes can sometimes cause what is known as Comatic Aberration (Coma).

This where images are distorted and blurred and not in sharp focus (like a star with a tail).

Catadioptric telescopes on the other hand, do not run into these issues because they utilize both the Refracting and Reflecting optical design.

However, due to this design and construction, Cassegrain telescopes come at a higher price. They are built with higher quality materials, so it is not really a surprise that they will be more expensive (even when at the same Apertures as other types of telescopes).

Cassegrain Reflectors and Cassegrain Catedioptrics work in different ways, the former utilizes your classic Reflecting technology and mechanisms. The latter is using the best of both designs.

Dobsonian vs Cassegrain (Differences)

The Dobsonian and Cassegrain are some of the most popular types of telescopes. There are some major differences that will help you to select the right one for you and your preferences:

Focal Length

Reflector telescopes, including Dobsonians, typically come with a shorter Focal Length compared to Cassegrain telescopes (that have a longer Focal Length).

What does this mean – the longer the focus, the higher the magnification.

Weight

Due to the glass materials used in its design, a Cassegrain is going to be heavier than a Dobsonian. This will obviously impact its portability.

Image Brightness

From my experience and research prior to purchasing my own telescope, Dobsonian telescopes tend to provide brighter images.

Cassegrain telescopes will not give you poor images, but a Dobsonian is likely to give you more vibrant and colorful images.

Now this list is no exhaustive and are just some of the main differences. If you ever get the opportunity to use a Dobsonian and a Cassegrain then I am sure you will discover more!

Conclusion

The Dobsonian is the easiest to use and most affordable telescope design; I can see why it has become so popular for astronomy beginners.

While a Cassegrain is an excellent choice and in some ways superior due to its reflecting/refracting optical design and better materials, it comes at a much higher price.

Another significant reason that a Dobsonian is easier to use is due to the Alt-Azimuth mount and the ability to observe Deep Space Objects (DSOs) including Nebula and Galaxies.

However and ultimately, it all comes down to preference, experience, and what you want to observe.

There is definitely a place for a Cassegrain if you have more years of experience in astronomy on your side.

If you are in the market for a new telescope, be sure to check out my comprehensive buyers guide. I outline what all the terms and specification means, what to look for and the pros and cons of each model. I’ve also compared spec side by side and taken into account user experience, reviews and results.

1 thought on “Dobsonian vs Cassegrain [Difference Between the Telescopes]”

  1. As a 65 year old Science teacher considering a first telescope (might become a retirement hobby), I appreciate the detailed compare and contrast, and really appreciate that it is not full of jargon confusing to a “newbie”. I feel I could go into my Science supply store tomorrow and make an intelligent purchase. Thank you!

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