These days you can find many types of telescopes on the market. But do you know what the very first type was? Yes, you guessed it right! It was the refracting telescope. Though being the simplest, it is still widely used for stargazing and other astronomical purposes.
In this article, we will dive deep and get a deep understanding of refracting telescopes. Then, we’ll look at what these are, how refracting telescope works, its advantages, and lastly, what its limitations are.
So, without further ado, let’s get started!
Table of Contents
What Is A Refracting Telescope?
Its lens is the main feature of a refracting telescope that distinguishes it from other telescope types. Refracting telescopes, also known as dioptric scope, solely use a lens to create images.
A refracting telescope consists of 2 lenses. One is at the eyepiece, and the other is the objective lens. The objective lens receives light rays from the source and focuses them on a single point. The image is formed at the focal point (the point where the light rays are focused).
After that, the eyepiece lens gathers the refracted lights and transmits them to the eye. Finally, the eyepiece lens is responsible for the magnification. It determines what the magnification will me. If you’ve read me how telescope eyepieces are measured post, you’ll know how changing eyepieces can change the magnification of a telescope.
Frankly, this is what a refracting telescope is. See how simple they are?
What Are The Parts Of A Refracting Telescope?
These are the structural components of a refracting telescope:
Objective Lens: Among the 2 lenses, the larger one is the objective lens. The objective lens sits at the front of the telescope and is responsible for gathering lights. Therefore, the larger the objective lens is, the more light it can collect. As a result, the image will be crisper and sharper.
Also, a bigger objective lens allows us to see deeper and fainter objects in the night sky.
Eyepiece Lens: The eyepiece lens is responsible for the telescope’s magnification. With telescopes, you can easily change the magnification by changing the eyepiece.
One eyepiece can offer 50x magnification with the same telescope, whereas another can offer 100x. However, you shouldn’t get overboard with magnification. A Refractive telescope has its limit.
In this post, I have explained how magnification is measured, how to calculate the limit of your telescope, and many other fundamental technical parameters for using any telescope.
How Does A Refracting Telescope Work?
As I have mentioned before, refracting telescopes have 2 types of lenses: the objective lens and the eyepiece lens.
The objective lens gathers light from the object we want to see (suppose the Moon). Then it bends the light rays and focuses them into a single point. This point is known as the focal point. The focal point is extremely important because this is the point where the image is formed. In this case, the image of the Moon will be formed at the focal point.
Then light rays from the focal point reach the eyepiece lens. As a result, the eyepiece lens magnifies the image formed at the focal point. As a result, different eyepieces can offer different magnifications of the same image formed at the focal point.
This is the simple working principle of a refracting telescope.
Quality Factors Of A Refracting Telescope
Do all refracting telescopes produce the same quality image? Now. The quality of the image, as well as the sharpness, depends on some factors.
Here are the quality determining factors of a refracting telescope:
How Good Is The Lens?
When it comes to the refracting telescope, everything depends on the lens. If the lens has poor quality, there is no way you can expect a higher quality image. The lens needs to be top-notch for a good quality image.
A cheap lens can have imperfections that will produce a distorted image. And the only way to fix it will be to buy a better lens. There is no alternative to a good quality lens.
How Large Is The Lens?
I have mentioned that the objective lens gathers light. The larger the objective lens is, the more light it will gather. Consequently, the crispier and sharper image the objective lens will produce. That’s why we should always prefer a refracting telescope with a larger objective lens.
I hope now you understand why a 12-centimeter lens is better than, let’s say, a 4-centimeter lens.
Do you know why we can’t read text from very far away? It is because the lens in our eyes (retina) is small and can’t gather enough light. If we could expand our retina size, reading a book from 10 meters away would be a piece of cake!
What Is The Magnification?
Magnification also plays an important role when determining the quality of a telescope. Every telescope has its magnification limit. Beyond that limit, the image gets distorted and blurred.
Magnification depends on many factors, including the size of the image produced by the objective lens and the focal length.
Stay within your telescope’s magnification limit for a clear image.
Advantages Of Refracting Telescope
- The revolving power is much greater than other types of telescopes
- Produces steadier images
- The light path doesn’t get interrupted
- Requires minimum maintenance
- Simpler structure
Limitations Of Refracting Telescope
The most common problem of refracting telescopes is chromatic aberration. This is the main reason why reflecting telescopes were invented.
Before getting to chromatic aberration, let’s learn some basics.
The light as we see it is not that simple. For example, white light consists of 7 different constituent lights. We can test this by passing sunlight through a prism. Isaac Newton was the first to find this out.
Now that we know the light is made of several constituent lights or wavelengths of lights let’s understand what chromatic aberration is.
We already know that the objective lens bends light into a single point. But as light is made of several wavelengths of other lights, each wavelength gets bent differently and focuses on a different point.
This results in a blurry and distorted image.
This effect is known as Chromatic Aberration.
You can lessen the effect of chromatic aberration by using telescopes with higher focal ratios. To know the focal ratio, divide the focal length by the aperture.
Dilemma With The Lens Size
If the lens size is small, the image quality will reduce. As I told earlier, the objective lens gathers light, which determines the image’s overall quality. If the objective lens is small, it can’t gather enough light. Consequently, the image will lose quality.
On the other hand, there is a problem with a larger objective lens too. A larger objective lens often faces lens sag. Lens sag generally occurs in the middle of the lens due to gravity. It leads to poor quality and distorted image.
My Favorite Refracting Telescope
If you are looking for a quality refracting telescope at a lower price, I’ll highly recommend Orion AstroView refracting telescope. I haven’t found any other refracting telescope that offers so much at such a low price point.
- Perfect for viewing Moon, planets as well as other deep sky objects
- The equatorial mount makes it easy to track any object
- It comes with an EQ-2 adjustable tripod
- Includes everything you need for a successful stargazing experience
So, if you want to try it, check out the latest price on Amazon.
So, this is all about refracting telescopes and how they work. I hope I’ve explained the working principle clearly to you. Though there are many more types of telescopes these days, refracting telescopes will always have their importance in astronomy and stargazing.