Is the primary purpose of an astronomical telescope to magnify objects in space?
No, it isn’t. Please read on to discover the actual primary purpose of a telescope.
Now, if you thought differently, don’t worry. It is a widespread misconception. And I suppose it’s easily done since telescopes make things look bigger than they actually are.
But believe it or not, magnification isn’t a telescope’s primary purpose.
The question of a telescope’s primary purpose may seem redundant, but most people get the answer wrong. And that is why I wanted to explain why telescopes are needed to study the night sky.
And trust me, once you understand it all, it’ll make selecting a new telescope much easier. So, are you ready to uncover the truth about telescopes? Let’s get straight to it.
If It’s Not To Magnify, Then What Is Its Purpose?
So, since we’ve established that an astronomical telescope’s primary purpose isn’t to magnify objects in space, what is its purpose?
A telescope’s primary purpose is to collect light.
That’s right; telescopes essentially collect a large amount of light. And that’s pretty much all there is to it (kind of).
When a telescope collects more light, dim astronomical objects become brighter, sharper, crisper and easier to see to the human eye.
How Does It Work?
Okay, so telescopes have curved lenses or mirrors that focuses light at the focal point of the telescope. Still with me?
The objective lens of a telescope forms an image near the focuser. The formed images become magnified by a smaller second lens called an eyepiece. The amount of magnification depends on the telescope’s focal length and the focal length of the eyepiece (for more information on this, see What Does The Number On An Eyepiece Mean?)
So you weren’t entirely wrong…a telescope still magnifies an image. It’s just not the primary purpose. .
Then you look through the eyepiece and see the bright, magnified image.
But without the collected of light from a larger objective lens or mirror, you would only see a magnified image that would be incredibly dim, fuzzy, and intelligible.
So, although magnifying the image is essential, it wouldn’t help us observe the universe very well alone. It also needs light and brightness to form a clear image that we can see.
And because of this, the diameter of the objective, also known as the aperture, is super important when gazing up into the night sky.
How Aperture Affects the Clarity of the Image
I will ask you to imagine that it’s raining outside and you must collect the water. You have a huge bucket to your left and a small mug to your right. The bucket and the mug are your ‘telescope’s’ objective lenses.
Which one is going to collect the most rainwater?
The huge bucket, obviously.
Well, it’s pretty much the same in terms of aperture and light. A lens with a larger diameter is going to collect more light than that of a smaller one. Ultimately the bigger your aperture, the clearer your image will be. Also, a larger aperture will allow you to observe dimmer objects.
A telescope can be referred to as a light bucket. However, instead of collecting rain, light buckets collect photons (i.e. light).
For this example, let’s imagine that we are looking at Jupiter. Below you’ll see an imageof Jupiter through a 2” lens (left) and a 4” lens (right). Each image is magnified 100 times (to discover how magnification is calculated, see How To Find Total Magnification). Can you see the difference?
Though these images are both viewing the planet using the same magnification, one is astronomically clearer than the other.
With the 2” lens, you can see just about the most prominent cloud belts. Overall, the image is still incredibly dim and fuzzy. You really can’t make out all that much.
However, the image with the 4” lens is much clearer. There are more distinct lines where you can see the belts, and the colors are much brighter and more defined.
You can see details of the planet that were not visible because of the lack of light due to the smaller aperture of the smaller telescope.
This proves that it is not the magnification abilities that allow us to see into space with detail but rather the amount of light collected through the telescope.
A telescope with a larger aperture (Also check out How To Adjust Aperture On Canon) will result in a more distinct and detailed view.
Choosing Your Telescope
I’m sure you can see how this information may change how you view purchasing a telescope. You’re not looking for a telescope that magnifies the best; instead, you want to opt for a larger aperture. Never buy a telescope that is marketed on what magnification can be provided. These telescopes are of poor quality, and you will be disappointed even at moderate magnifications.
The only catch?
As you can imagine, the larger the aperture on your telescope, the more it will cost you. And this can get very expensive. They also tend to be a lot heavier and more challenging to use.
So a huge aperture telescope might only sometimes be the best option, especially for beginners.
I recommend opting for the largest aperture within your price range. However, it would be best to consider that you’ll get a more narrow view of the sky than with smaller telescopes. For an adult, an aperture of 8” (200mm) provides the best of both worlds. You will be able to observe dim objects, and it is not too large to lug around and set up.
Choosing your telescope will come down to personal preference. But with your new-found knowledge, remember that the larger your telescope’s aperture, the clearer images you’ll get.
Final Thoughts
Telescopes do make incredibly far-away objects appear much larger. However, it’s a mistake to assume that the primary purpose of an astronomical telescope is to magnify objects in the sky. As we have learned today, this is not the case.
Of course, we still need to magnify those images to get a clearer picture of them. But this wouldn’t be possible without the ability to collect more light.
We’d see larger, closer-up fuzzy blobs of nothing if we didn’t have the aspect of light collection.
And that definitely wouldn’t help us to become more attuned to the great beyond.
Hi, my name is Jason Anderson, and I am a Physics Professor. Ever since I was a kid, I’ve been fascinated with space, the universe, the moon, you name it. I spent hours and hours at the planetarium close to my hometown, wondering what else could be out in the universe.
Since then, I’ve been an avid stargazer and astronomer, and love nothing more than spending my time charting stars, observing planets, and finding constellations.
This is why I decided to start Telescope Guru. I only wish to share this fun pastime with the world. With this site, I hope to answer all of your questions relating to astronomy, telescopes, and stargazing.
