How To Increase The Magnification Of a Telescope

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There are few options for how you can increase the magnification of the telescope. Telescopes come in a stock configuration, not using the maximum potential they have. You always have to buy some additional accessories if you want to increase the magnification.

The best way to increase the magnification of a telescope is to increase the focal length of a telescope with the Barlow lens or to use an eyepiece with a shorter focal length. You can also combine a Barlow lens with a short focal length eyepiece to get the highest useful magnification of a particular telescope.

There are rules you have to follow because every telescope has different specifications. Let me explain in detail so, in the end, you will know exactly how to increase the magnification of your telescope.

How To Calculate Telescope Magnification

The first thing you need to know is how to calculate the telescope magnification. You will need your telescope’s specifications to do this—mainly the focal length, and secondly, what eyepieces you have. 

To calculate the magnification, you have to divide the focal length of the telescope by the focal length of the eyepiece you will use with it.

Telescope Magnification Formula:

Now, when you look at this formula closely, you should see that if you want to increase the telescope magnification, you have to increase the focal length of the telescope or decrease the focal length of the eyepiece.

Increasing Telescope Magnification With The Eyepiece

Telescope Eyepieces

Let’s start with a change of an eyepiece focal length and see what magnifications you can expect from different eyepieces. The telescope magnification formula will tell you what the magnification of the telescope with a given eyepiece is. 

For example, if you have a telescope with a focal length of 1000mm and you have two eyepieces with a focal length of 10mm and 20mm, the telescope will give you two magnifications to use.

Dividing the 1000mm focal length by 10mm and 20mm eyepiece results in 100x magnification with 10mm eyepiece and 50x magnification with 20mm eyepiece.

As you can see, it is essential to have more eyepieces if you want different magnifications. Using a shorter focal length of the eyepiece is increasing the magnification of the telescope.

You can also buy a special zoom eyepiece. It is a single eyepiece where you can adjust the focal length by turning the barrel—something like the camera lenses. 

The advantage of the zoom eyepiece is that you have only one eyepiece, and you don’t have to change it in the focuser when you need to use another magnification. It is also a cheaper option than owning a bunch of different eyepieces.

The common focal length range with the zoom eyepieces are 7mm to 21mm and 8mm to 24mm. The Baader Planetarium 8-24 mm Mark IV Hyperion Universal Zoom is a recommended choice.

Increasing Telescope Magnification With The Barlow Lens

Barlow Lens

Let’s play now with the focal length of the telescope. If you want higher magnification, you can also increase the focal length of the telescope. However, the telescope’s focal length is fixed, which means if you want a different focal length, you have to buy a different telescope. Right?

Actually, you don’t have to because there is an optical tool called Barlow lens that can increase the focal length of the telescope. Barlow lenses come in different specifications and can only increase the focal length of the telescope. 

They have a multiplier, which tells you how much a Barlow lens will multiply the focal length and increase the telescope’s magnification.

Barlow lens can have a 2x, 3x, 5x multiplier. These are standard Barlow lenses you can buy. 

Let’s use a 3x Barlow lens in our example with a 1000mm telescope and two eyepieces of 10mm and 20mm. The 3x Barlow lens will triple the focal length of the telescope from 1000mm to 3000mm.

Using these new numbers in the telescope magnification formula, you get 300x magnification with the 10mm eyepiece and 150x magnification with the 20mm eyepiece.

The Barlow lens is a must-have tool if you want to increase the magnification of the telescope. It is also cost-effective because, as you can see, you will be able to use four different magnifications- 50x, 100x, 150x, and 300x with only two eyepieces and one Barlow lens.

Using a Powermate will yield you the same results, and you can learn more about the difference in my article: Powermate vs. Barlow Lens.

Pick your Barlow lens here: Best Barlow Lens – Buying Guide.

What Is The Highest Useful Magnification And How To Calculate It

The magnification of every telescope has a limit. It is called the highest useful magnification. Going beyond that limit is going to result in a too dim and blurry image.

Every telescope has a different limit, which is determined by its aperture size. Aperture is the diameter of the primary mirror or lens, depending on what kind of telescope you’re using.

The rule is that the highest useful magnification of the telescope is 50x the aperture in inches. If you have a telescope with a 5inch aperture, the highest useful magnification is 250x. A telescope with a 10inch aperture will be able to give you 500x magnification.

It is crucial to know, and you have to consider this when increasing the telescope magnification with the Barlow lens or eyepiece. Do the calculations before you buy any additional accessories, so you don’t go over this limit and waste your money.

Anyway, even if your telescope has a big aperture, don’t go to high numbers because you can only use around 200x magnification in real life. This limit is caused by the atmospheric turbulence, and there may be only a few rare nights where the seeing conditions are perfect, and you can go over this limit, probably up to 300x.

What Is a Good Magnification For a Telescope?

The good magnification for the telescope is, in fact, a variety of different magnifications. Every object in the night sky needs to be observed with a different magnification.

For example, planets need high magnification because they are small. The moon is also better in high magnification because you can observe beautiful surface details and craters.

On the other hand, deep-sky objects like nebulae are big and require less magnification to fit in the field of view. So it is a good idea to have more eyepieces with different focal lengths to choose from if you want to observe different types of objects in the night sky.

Is magnification or aperture diameter more important when selecting a telescope?

You will be surprised, but the magnification of the telescope is not as important as the aperture. The reason is that the bigger aperture can collect more light and provide greater details of the object. But many deep-sky objects are so big that you have to observe them with lower magnification.

Most of the objects in the night sky are very dim, and you need a big enough aperture to see any details. Using high magnification with a small aperture is not a good idea. Always prioritize the aperture on the telescope.

As you learned here, increasing the magnification is not complicated, and a big aperture will give you better image quality in high magnifications.

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