Buying your first telescope can be confusing. The amount of information about telescopes seems as endless as the universe itself. To help with this, we have put together a handy beginner’s guide in four parts. This section will introduce you to the basics, and the others related to the age of the owner – child, teenager or adult. So after this part, skip ahead to whichever section is relevant to you.
What is a Telescope Anyway?
The primary purpose of telescope is to collect light from objects that are very far away, and too dim for us to see with our naked eye. The collected light can then be viewed with an eyepiece directly by the observer (you!) or directed onto a camera to create an “astrophoto”.
Where do I Start?
Well this is a good place! Apart from online resources, reviews, forums etc we can also recommend a visit to your local astronomy club. Amateur astronomers are often more than happy to let you have a look through their telescopes, and talk your ear off about everything space related.
Eventually though, you’re going to have to take the plunge, and buy your first telescope. Nothing beats learning while doing!
Aperture is a word you will hear a LOT. It is the diameter of a telescopes main optical component (either a lens or a mirror). The aperture of a telescopes tells you how bright (light gathering ability), and sharp (resolving power) an object will be. When it comes to aperture, bigger is often better: a bigger aperture will let in more light!
Another important thing to consider when buying a telescope is its “power” or magnification. The magnification is determined by dividing the focal length (the distance from the primary lens or mirror to the image it forms) of the telescope by the focal length of the eyepiece. Every telescope will tell you it’s focal length, as well as its maximum and minimum useful magnification.
Field of View or (FOV) is the area of sky visible through an eyepiece, measured in degrees. As you increase the magnification on your telescope, your field of view will decrease. It’s an important consideration when choosing which eyepiece to use. Large celestial objects require a lower magnification with a wider field of view.
Don’t worry if all this doesn’t make a whole lot of sense just yet. Generally speaking, the higher these numbers the better. Except for one : The F-number, which is the ratio of aperture to focal length. For this number – lower is better! Think of it as the “speed” of the telescope. Basically, the lower the number, the brighter things will appear. Or put another way, the lower it is, the faster it collects the light.
What Am I Going to See?
Naturally, it depends which telescope you buy. A larger the aperture equals more light meaning you’re going to be able to make out objects that are dimmer and further away. However, even the simplest telescopes are going to show you fantastic views of our moon and the planets; including the moons of Jupiter and the rings of Saturn!
Keep in mind that when you look through some telescopes, such a refractor telescopes, the image will be upside down! No need to worry, this is just how the different lenses work, and it can be corrected with the use of an erecting prism if desired.
Another thing to consider is colour. Because the human eye cannot see colour when it’s especially dim, deep space objects will appear to be black and white. Other celestial objects such as stars and planets will appear in colour, however, not the bright colours you’re used to in textbooks and magazines.
Why do Planets Appear so Small?
Planets are small bodies that orbit around stars. When you look through a telescope, they will appear small. As an example, in a telescope, Jupiter will fit 45 times in a half degree field (about the size of the full moon!). For observing planets, a big field of view is not important. However, resolution is important for planets. You should use as much power as your telescope can clearly resolve. How much detail you can see will depend on the aperture of your telescope.
What are the Different Types of Telescopes?
There are many different kinds of telescopes available. The two main types are refractor, and reflecting telescopes.
Refractors: The Ultimate Grab-and-Go Telescope!
When picturing a traditional telescope, chances are you are thinking of a refracting telescope. First invented in the Netherlands in the 1600’s and propelled to fame by Galileo Galilei, the refracting telescope utilises a carefully made lens system that relies on the bending of light to produce beautiful images on the night sky; especially the planets!
The majority of refracting telescopes use two lenses: the objective lens at the front of telescope, and a smaller lens in the eyepiece. Their simple design means that refracting telescopes are low maintenance, easy to use, and highly transportable.
However, there are some draw backs. Tube lengths can be unpredictable. For example, a “4-inch” refractor may be over a meter long!
Also, because the eyepiece is at the lower end of the tube, this might make viewing difficult, and a tall sturdy tripod may be required for viewing, which can add cost to your telescope. If deep sky viewing (Galaxies, Nebulas) is where your interest lies, a refracting telescope may not be for you, as they do not let in enough light to make out faint objects.
That said, modern optical designs have led to smaller, more manageable telescopes making newer refracting telescopes the ultimate grab-and-go back-yard telescope!
Reflectors: Best Value for Money!
In the later 17th century, Scottish astronomer James Gregory proposed a telescope that used a complex system of mirrors to produce a cleaner image of the sky than refractors of the day. It would take five more years for the telescope to be built by English Mathematician and apple enthusiast, Sir Isaac Newton.
“Newtonian” reflectors contain two mirrors: a large curved primary mirror at the bottom of the tube, and a small elliptical shaped mirror near the top. The small mirror directs light from the primary mirror through a conveniently placed eyepiece. Their compact but complex design means that these telescopes are great value for money. The best value reflector for viewing is arguably the Dobsonian Reflector telescopes. These reflectors come with a sturdy mount making casual viewing a breeze. Dobsonian telescopes start at 4 inches and go all the way to a massive 30 inches. Perfect for your own observatory – but not small!
Luckily, even if you’re not planning to make your own observatory, reflectors come in many shapes and sizes; from long tubed Dobsonian to small compact Newtonians. Unlike refractors, all reflecting telescopes require occasional maintenance; the small secondary mirror can come out of alignment if the telescope is bumped or jostled when being transported. This is easily solved by collimating your telescope, however, this can be time consuming and frustrating for beginners at first. Once learned, the effort is rewarding. The reflectors open tube design also means that both lenses will require cleaning as dust and dirt are likely to accumulate.
Reflecting telescope designs provide you with sharp, crisp images of all manner of celestial objects. From our small neighbouring planets to intergalactic behemoths; the reflecting telescope can see it all!
Combination telescopes: The Best of Both Worlds!
For centuries the refracting and reflecting telescopes were your only options for interplanetary viewing. It wasn’t until the 1930’s when German astronomer Bernhard Schmidt discovered that you could combine the best characteristics of refractors and reflectors. Employing both mirrors and lenses, the catadioptric or compound telescopes give you the best of both worlds.
Schmidt’s realisation that you could combine a primary mirror at the back of the telescope with a correcting lens at the front ultimately led to the development of the Schmidt-Cassegrain telescope, or SCT. In an SCT, light enters at the top of the tube, bounces off the primary mirror at the back of the telescope, reflects off the lens at the top of the tube, and is directed down an eyepiece at the base of the telescope. In the end, you wind up with a telescope that is compact in size, but has a long focus length. Like their reflecting counterparts, the SCT does need collimation. However, unlike reflectors, they have a closed system making cleaning a breeze.
The SCT’s are highly versatile and very portable, however, as they are can be highly “technologized” they can be expensive. But if astrophotography is in your future, buying an SCT is perfect place to start!
The Importance of Mounts
When we use the word telescope, we’re actually referring to two different parts: an optical tube and the mount/tripod you stick it on. To get stable, good quality images, a sturdy mount is key. There are three main kinds of mounts: Alt-azimuth, Dobsonian, and Equatorial. The can be motorised, or not, and some also into GOTO. For those willing to spend the extra for a motorised GOTO mount, astrophotography becomes a possibility. As the sky appears to move, a GOTO mount will not only find distant objects for you, but track the sky to keep your target in frame.
Generally speaking though, if photography is not the goal, then equatorial, computerised, motorised GOTO mounts are not necessary. The simplest mount, and the best mount for beginners, is the Alt-azimuth. The name refers to how the mount moves: up and down (altitude), and left and right (azimuth). Easy! The Dobsonian mount is a newer type of Alt-azimuth mount that is specifically designed for Dobsonian telescopes.