Types of Telescopes – What are the differences?

Observing the space is truly a wonderful hobby and in some cases a very fulfilling and rewarding profession. Since it can’t be done with the naked eyes, we need special tools called ‘telescopes’ to do that.

However, what type of telescope we are using will determine every aspect of our experience. Today we’re going to talk about numerous types of telescopes that are gracing both physical and online marketplaces. This way, you can be informed about the options before considering whether to purchase a telescope or not.

Telescope Types – What to Know

There are more than 30 types of telescopes spread across the main categories, so we’re going to leave out certain types that are almost completely obscure. The three main groups where these sub-categories and types fall into are Refracting Telescopes (or Dioptrics), Reflecting telescopes (or Catoptrics), and Catadioptric Telescopes (Catadioptrics).

Refracting Telescopes

Refractors are optical telescopes that utilize lenses as a form of objective in order to form visual images of celestial objects. Basically, refracting telescopes are giant spyglasses outfitted with long-diameter lenses and apertures. It’s one of the earliest types of telescope designs pioneered during the 17th century.

These telescopes are named as such because their main principle of operation is ‘light refraction’. Refraction is defined as ‘the directional change of (in this case ‘light’) waves that pass from the primary medium to the secondary medium, resulting in a gradual change of the medium.  ‘Refraction’, in this sense, means ‘redirection’.

Achromatic Telescope

The Achromatic scope can be described as a direct response to the problem most refractors have to deal with –chromatic aberrations. Namely, achromatic telescopes got named after the type of lens they come supplied with (achromatic lens); it is specifically used to eliminate smudges, blurs, and trails caused by gradual chromatic aberration.

Some of the most popular designs of achromatic telescopes are Littrow doublet, Fraunhofer, Clark doublet, Oil-spaced doublet, Steinheil doublet, and others. These designs are basically different from one another in terms of minor tweaks to the original design.

Galileoscope

Galileoscope is basically a miniature refractor that was not designed for long-range space observation at all. It was invented a mere decade ago, and people could gaze at the planets closest to earth, a ‘handful’ of stars, or at the moon with it. The original design features an achromatic lens and suffers from severe chromatic aberration.

Non-achromatic telescopes

Essentially, the earliest designs of refractors were non-achromatic telescopes. These models are today only available in museums as they have minimal functionality and bear almost no value in terms of actual on-field use.

Reflecting Telescopes

Reflectors were invented shortly after refractors, and some people suggest that their design was an improvement of its predecessor. The main difference between reflectors and refracting telescopes is that the former utilizes mirrors while the latter utilizes lenses.

Reflecting telescopes are often linked with Newtonian telescopes, although somewhat wrongly because there are significant differences between these two groups.

The main principle of reflectors is ‘light reflection’ – these telescopes ‘reflect’ light waves. They are a bit harder to configure and set up, but they also eliminate most chromatic aberrations and are more suitable for long-range space observation.

Cassegrain Reflector

Cassegrain reflector telescope is one of the most popular reflectors available. It typically utilizes two mirrors (a concave one and a convex one) to amplify its usable magnification potential. These telescopes are usually installed in a place where they are meant to remain stationary, but at the expense of mobility, they provide superb optics.

Crossed Dragone

The Crossed Dragone scope is, in essence, an off-axis scope supplied with a parabolic mirror. Its main benefit is the preservation of light via polarization; most models are fairly light and highly transportable, which are the main reasons why people who are on a tighter budget tend to opt for them.

Newtonian telescope

Or in other words ‘the original telescope invented by Isaac Newton’. The design of this telescope is several centuries old, but it was so magnificent that it endured the test of time to this day. This is a reflector that utilizes a concave mirror and a diagonal mirror to collect and reflect light waves with pinpoint accuracy.

One of the most popular variations of the Newtonian Telescope is the famous Jones-Bird telescope, although most modern brands have a tendency to put their own stamp on the models they manufacture and distribute by adding minor tweaks and modifications (to the optics and mount mostly).

Three-mirror anastigmat

Just like the name implies, the Three-mirror anastigmat utilizes three mirrors that aim to completely eliminate the negative consequences of chromatic aberration. Even though these telescopes boast exceptional optics quality, they’re typically big, bulky, and somewhat unwieldy.

Catadioptric Telescopes

Catadioptric telescope is a hybrid type of a telescope that borrows the characteristics of Reflectors and Refractors. These telescopes utilize both lenses and precisely shaped mirrors to ‘reflect’ and ‘refract’ light waves. The main benefit of such an approach is superior error correction while chromatic aberrations are almost completely non-existent.

Argunov-Cassegrain telescope

This is a moderately modified Cassegrain telescope that was designed by P. Argunov in 1972. It utilizes spherical optics, which is vastly superior to other types of optics, and the amount of light they can gather is staggering.

Argunov-Cassegrain telescopes are fairly complex in structure and design, which makes them a relatively unpopular choice.

Maksutov telescope

Maksutov telescope is sometimes referred to as ‘Mak’; this is a catadioptric telescope that utilizes both spherical mirrors and meniscus lenses. This telescope addresses the chromatic aberration issues such as the ‘coma’ by regulating axis positions automatically. Although this is an old design, it’s still in use even today.

Conclusion

Apart from the categories we’ve mentioned, there are also numerous others scattered across Dioptrics, Catoptrics, and Catadioptrics, such as dialytic refractor, Apochromatic telescopes, Copyscopes, Gregorian telescopes, Large-Liquid-Mirror telescopes, Pfund telescopes, and many others.
For as long as you’re well-acquainted with the three main groups, including Refractors, Reflectors, and Catadioptric telescopes, you’ll be able to notice that the differences between the main types and their derivatives are minor at best. We do, however, encourage you to dig up as much info as you can on all these telescope categories; who knows, maybe an obscure telescope might be just what you were looking for.

About Derek

Hey! I'm Derek, I've been interested in astronomy since.. well, forever! I'm an engineer by trade, but I've been playing around with telescopes for many years. I hope to impart some of the knowledge I've learned over the years onto you!

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