This article gives you a rundown on the three types of telescopes you can buy on the market, including those that can be categorized within the types. It also will go over the most important aspects of a telescope, and what to look for!
This article only goes over the telescope optical tubes, if you want to go over the mounts and other accessories, you can read about those in this article.
The Three Types
Refractor – uses lenses.
They are low maintenance, tend to be smaller and very light weight, hence they are very portable. They also give you the sharpest images of any of the three types of telescopes.
However, it costs more to make a glass lens than a mirror, so once you get into wider refractors, there is a huge spike in prices. All refractors also suffer from chromatic aberration, as through an optical lens, different colored light bends at different focal points, which means you may see some red and blue halos around certain objects. Unless the refractor is good quality and has the corrective lenses that help that problem, you will have to deal with it.
Reflector – uses mirrors.
They are capable of being wider, and are much more economical in terms of pricing. It should be noted that all of the world’s largest optical telescopes use mirrors, and their nickname of “light bucket” serves as a reminder of their capabilities over a refractor.
Most reflecting telescopes on the market are made in the Newtonian design, where you see the eyepiece placed near the front of the tube, rather than the back. Other reflectors, such as Gregorians or Cassegrains have the eyepiece at the bottom.
Some cons are that they require a bit of maintenance and care to keep working properly. Since their optics are at the bottom of an open tube, you need to watch out for tube currents and any moisture or dust that can collect on the mirror.
Newtonians can also prove difficult with eyepiece placement, as sometimes, after slewing your telescope to where you want to observe, the eyepiece can be angled out of reach, or almost upside down, causing a loose eyepiece to fall off if not tightened properly. You can still loosen the tube and rotate the tube to make the eyepiece angle comfortable, but that can move the tube slightly out of alignment.
Catadioptric – uses both.
A Catadioptric telescope is primarily a reflecting telescope, but due to their design they can be categorized on their own due to the inclusion of a corrective lens, called a “correcting plate” at the front of the tube. Essentially, reflection and refraction are combined into a single system.
Schmidt-Cassegrain telescopes are very popular catadioptric scopes. It comes from the pairing of a Cassegrain designed reflector with the Schmidt correcting plate.
Maksutov-Cassegrain telescopes are similar, except the corrector plate is a different type and curved inward.
Catadioptic telescopes by their design can be wide, yet compact, making them much easier to transport than say a larger Newtonian. Their main con is that their prices spike by a high factor when increasing aperture. While smaller catadioptrics can pack a punch, the more affordable models barely collect enough light for deep sky objects. Wider catadioptrics on the other hand will easily set you back four figures.
Most Important Specifications
Aperture – Light Gathering Power
The aperture is the number one thing a telescope must have. How much light the telescope can collect not only determines how bright an object looks, but how well you can resolve finer details. . With the moon and planets, the larger telescopes will show finer detail than the smaller telescopes, and a deep sky object will appear much brighter and show more contrast than they do on smaller telescopes.
Focal Length – How the Image Appears
The focal length determines how wide or narrow your field of view is, and it also determines your magnification factors when using certain eyepieces. Shorter focal lengths allow wider views in your field of view, thus you see more of the sky, while longer focal lengths give a narrower field of view.
If you want to use the telescope for prime focus photography, the focal length essentially turns the telescope into a camera focal lens of that value!
Magnification – How Much Can You Zoom?
The magnification comes from the eyepieces and lenses you’re using, not from the telescope itself.
Magnification is determined by the focal length of the telescope divided by the eyepiece. A 10 mm eyepiece being used with a 500 mm telescope wields 50x magnification, while the same eyepiece in a 1000 mm telescope wields 100x.
Where to Start For Beginners
As stated before, it’s the aperture, not the magnification, that is the most important factor for any telescope!
Most beginner telescopes are between 60 – 114 mm in diameter, or 2.3 – 4.5 inches. In terms of cost wise, reflectors will cost much less compared to refractors due to the cost of making lenses being more expensive. Affordable catadioptrics such as a small Maksutov won’t have much aperture either.
It all will go down to what your personal needs are.
How serious are you about getting into owning a telescope? Who is this for? What do you want to be able to do with it? What do you hope to see?
If all you want to do is view the Moon and planets, then a refractor will be better suited for that.
If you want decent views of deep sky objects like nebula, clusters, and galaxies, then a larger reflector will be great for that.
If you just want an all-round telescope, then just consider going with as wide of aperture and let everything else come later.
But What’s the Cost?
Most good quality beginner telescopes are in the $200 range. Depending on what you get, you can have a good long term investment to serve your needs, or it will be a short term stepping stone into something bigger.
The following article gives you a better idea on what to expect: What Can $200 Get Me On A Telescope Budget?