How Do Different Types Of Telescopes Work?

What type of telescope should I get? If you want to look at stars or planets, then you’ll probably need a refractor.

If you want to see deep space objects, then you’ll need a reflector. And if you want to view things close up, then you’ll need an aperture.

How Do Different Types Of Telescopes Work

Telescopes come in various shapes and sizes. Each has its advantages and disadvantages, depending on what you want to observe.

For example, a refractor allows you to see both distant and near objects, whereas a reflector only lets you see far away objects.

We look at the different types of telescopes you can get and their differences in how they work, to help you decide which one might work best for you.

How Does A Telescope Work?

A telescope is just a lens that focuses light from a star or planet onto your eye.

Well, actually, it’s two lenses: A primary lens (also called the objective) and a secondary lens (called the eyepiece).

The primary lens gathers light from an object and directs it into the secondary lens. The secondary lens then sends this image to your eye.

The size of these lenses determines how much light gets through them. Lenses with bigger diameters gather more light than smaller ones.

So, a telescope with a larger diameter will let in more light than one with a smaller diameter.

The focal length of a telescope refers to the distance between the primary and secondary lenses.

The longer the focal length, the farther apart the lenses are. The shorter the focal length, the closer together the lenses are.

The focal length also affects magnification, which we explain below.


When you use a telescope, the amount of light coming through the primary lens is magnified by the secondary lens.

Magnification is calculated as follows:

Magnification Diameter Of Secondary Lens / Focal Length

For example, if you have a 10-inch (25cm) telescope with a focal length of 100 inches (250 cm), you would multiply the diameter of the secondary lens by 1/100 to calculate the magnification. In other words, 10 x 1/100 0.1.

That means that when you look through the telescope, the image appears about ten times larger than it does without the telescope.

How Do Different Types Of Telescopes Work?



Refractors are the most common kind of telescope.

They were invented in 18th century England, where they were used to study the sun and the moon.

These early telescopes had very large lenses, and they could be built quite cheaply. Refracting telescopes refract or bend light.

Glass makes up the objective lens, which is the big and round plate of glass at the front of the telescope.

This is where you can measure the aperture or the size of the objective lens.

It’s responsible for light-grasp, and this simply means how much light can be collected within the tube.

Light enters through the lens and is split up into wavelengths.

They travel through the tube and meet at a focal point where a telescope diagonal allows for that light to be focused on the eyepiece.

Refractors are still popular because they’re easy to build and maintain.

However, they don’t allow you to see as many details as modern telescopes do.

Because of this, they aren’t ideal for observing faint objects like galaxies and nebulae.

Refractors typically have 6 inches (15cm) to 12 inches (30cm) diameter lenses.

Their focal lengths range from 30 inches (75cm) to 150 inches (375cm).

Refractors are inexpensive, but not very powerful.

You may need an alternate telescope to view small objects such as distant planets.

A good example of a modern refractor scope is this Celestron AstroMaster 70AZ.


Reflectors are similar to refractors, except that instead of using glass lenses, they use mirrors.

Mirrors are more expensive than lenses, but they can collect more light.

Reflectors have a primary mirror that is situated at the bottom of the telescope.

At the top of the reflector is a secondary mirror, and to the side, you will find the eyepiece and focuser.

Light enters the tube and reflects off the primary mirror towards the secondary mirror.

The secondary mirror can then direct the light towards the eyepiece.

This mirror blocks a section of that incoming light from reaching the primary mirror.

Reflectors come in three different sizes: 4 inch (10cm) to 8 inch (20cm) diameter; 9 inch (23cm) to 16 inch (40cm) diameter; and 20 inch (50cm) to 32 inch (80cm) diameter.

Reflector telescopes are usually more expensive than refractor telescopes. And they’re often better at viewing faint objects.

But reflectors are harder to work with than refractors.

You have to carefully position your eye close to the eyepiece or risk missing out on what’s happening in front of you.

An example of a high-quality yet affordable reflector scope would be this Celestron AstroMaster 114EQ.


A Cassegrain telescope uses two mirrors to form its optical system.

One mirror focuses the incoming light onto another mirror, which then reflects the light through the first mirror.

The result is a much brighter image than you’d get with just one mirror.

This means that this telescope uses a primary parabolic mirror and a secondary hyperbolic mirror to reflect the light through a hole.

The secondary mirror produces a folding effect, which creates a telescope with a shorter tube length with a long focal length.

The advantage of this design is that you can easily correct for atmospheric effects.

So even though you’re looking through a long tube, you won’t lose any detail due to turbulence in Earth’s atmosphere.

The disadvantage of Cassegrain telescopes is that they’re more difficult to make than refractors, and, as such, they tend to cost quite a bit more.

A typical Cassegrain telescope has a focal length between 50 inches (125cm) and 100 inches (250cm).

It also has a maximum aperture of about 15 inches (38cm).

Cylindrical Lenses

Cylindrical Lenses

Cylindrical lenses are made up of thin layers of transparent material stacked together.

When light passes through these lenses, it bends slightly. That’s why they’re called “cylindrical.”

Cylindrical lenses are used in most large astronomical telescopes.

They’re also sometimes used in smaller telescopes to produce special effects.

For example, when you look through a pair of binoculars, you see double images because each lens bends the light twice.

Cylindrical optics are relatively easy to manufacture. However, they’re not nearly as versatile as other types of lenses.

You can buy an average-quality 10 inch (25cm) to 12 inches (30cm) diameter telescope for under $100.

These telescopes are useful for observing bright celestial objects like Jupiter and Saturn.

Folded Refractors

A folded refractor is a type of telescope that uses curved mirrors rather than lenses.

Like a regular refractor, a folded refractor forms an erect image by bending the light coming from the object.

But instead of using a single concave mirror, a folded refractor uses two flat mirrors that are placed side by side.

Each mirror is shaped so that it reflects the light toward the next mirror.

Eventually, all of the light comes back to the same point where it started.

Folded refractors have a focal length between 30 inches (76cm) and 60 inches (152cm), and a maximum aperture of about 8 inches (20cm).

Final Thoughts

We hope after reading this article you have learned a little more about how a telescope works and what different kinds of telescopes are out there to allow you to explore our solar system.

Remember, each telescope comes with its advantages and disadvantages, so make sure you weigh these out before purchasing, and you’re sure to end up with the perfect one suited for your astronomical needs.

Gordon Watts