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What Is a Good Magnification For a Telescope [What Do I Need?]

If you are looking at buying a new telescope or a new eyepiece, odds are, that you’re going to have to choose between different magnification.

You’re also going to want to learn everything you can about the other spec that dictates the power of the scope, and what components are included,  before you make the purchase.

So, what is a good magnification for a telescope? A good magnification for a telescope will be the one that provides you with the image density and clarity that you desire. In other words, the best magnification for you will be the one that lets you observe the objects in the night sky you want and at the level of detail you want to see them.

More magnification is not necessarily better it depends what you want to see and when.

In many ways astronomers typically seek a lower magnification. This is especially true for beginners when starting out.

Does this sound too vague? Well, that’s because what is a good magnification for you may not be for somebody else.

Here’s why…

What Is Magnification? 

In simple terms, magnification is the ability to increase the size of an object in the distance. It ultimately gives you the ability to observe an object more closely.

Magnification is defined in …x, or how many times larger than it appears with the naked eye.

So a telescope with a 50x magnification shows the object at 50 x its original size as observed by the naked eye.

So, do you even want to see a planet/star more closely and in greater depth? That’s a question that you will need to ask.

Thankfully, telescope manufacturers have understood this varied need and preference.

At the lower end, telescopes typically begin with a 20x magnification and scale all the way to up to 300x!

There’s a lot of range here which is why one telescope can provide a completely different view and experience than another.

Now that you know what magnification is, you probably still have a few more questions.

For the remainder of the article, I’m going to go more in depth on some things to consider with magnification and when you would want low-magnification and high magnification.

I’ll also provide some suggestions on what may be the best magnification for you.

Lets begin with Eyepieces, as they are the one piece of the puzzle:

Eyepieces and Magnification

The exact component on a telescope that dictates the level of magnification is the Eyepiece. This is also an integral component that dictates the field of view (or how much width of the sky you see at any one time).

For these reasons, different eyepieces are used by astronomers to observe different objects in the night sky; utilizing the differing abilities to magnify.

For example, objects like Nebulae and Star Clusters typically appear large.

Therefore, it is advised to use low magnifications (which give a wider field of view) for the best views.

Planets on the other hand, appear very small so a high-magnification eyepiece will be more appropriate.

It is important to remember and understand that magnification is not the only, nor the most important, element to a telescope.

Instead it is the Aperture (or diameter) of a telescope will dictate its overall power.

Using different eyepieces is the key to getting the best views of the sky and the many objects in space.

Nearly all telescopes provide you with the ability to change eyepieces to get different magnifications.

Low magnification tends to give the best views, but always consider what you want to look at before making a decision.

How Does Magnification Work (How Is It Calculated)

Now you know what component of a telescope is responsible for magnification, its now helpful to understand how it works.

Now, Eyepieces are reliant on their Focal Length (every eyepiece has one and they are a few millimeters in length – this number is inscribed onto each eyepiece).

The Focal Length gives you an insight into the magnification when used on a certain telescope.

Here is how magnification is determined:

Magnification = Focal Length of the telescope ÷ by the focal length of the eyepiece.

So, the smaller the number that you find on an eyepiece, the higher magnification it will provide.

In this way, a 10mm eyepiece gives double the magnification of a 20mm eyepiece.

Now here is where it can get kind of tricky. Every eyepiece will provide a different magnification when it is used on a different telescope. This is something you will need to consider.

For example, a 10mm eyepiece would not provide much magnification when used on a short-focal-length telescope. It would provide quite a lot of magnification when attached on a long-focal-length scope however.

Continuing the example, on an 80mm short-focal-length refractor, the same 10mm eyepiece could only supply a  of 40x.

Yet if it was added to a 10″ Schmidt-Cassegrain telescope , the magnification could be as much as 300x!

Quit a difference huh?

So how do you use this information?

If you are buying an eyepiece, you need to identify what it will provide on your current telescope.

If you are buying a new telescope, you need to identify what eyepieces are provided and what magnification they provide (this is usually stated).

Eyepieces usually come together in a pack of 3. This is especially true when you buy a telescope and many brands include different eyepieces for use on that telescope.

You will find that three eyepieces are provided for different magnifications. One will be low power, the other medium, and the final one will be high power.

What magnification they provide depends on the telescope you choose, however, for the majority of telescopes this tends to be from 30x on the low-end to 300x on the high-end.

You can therefore use each eyepiece as required and interchangeably depending on what you want to observe.

Another good practice and something to consider – the maximum useful magnification of a telescope tends to be around 50x the aperture in inches.

If this ratio is any higher, the image viewed will appear very dim and blurry to be observed properly.

Thus, a 4-inch scope can provide about 200x magnification before images become too blurry and dim, a 6-inch scope is around 300x, etc.

Why High Magnification Is Not Always Better

Contrary to popular belief (especially by new astronomers), high magnification is not always better and there are several reasons for this.

This belief stems from the common assumption that if you want to view something far away, you need to magnify it more to see more.

However, the majority of objects in the night sky appear very big.  The Orion Nebula and Andromeda Galaxies are good case examples.

The former looks double the size of the Earths moon, and the latter appears six times larger.

Now even though the Andromeda galaxy is 70 trillion times further away than the Earths moon, it is also 420 trillion times bigger!

As a high magnification provides a smaller field of view, this means a large object is not likely to fit into the view of the telescope.

A second reason for keeping the magnification lower than logic suggests, is due to image brightness.

The law of physics means that doubling magnification leads to an image becoming four times dimmer.

When observing objects in the sky, be cognizant of the objects that are very faint to begin with (deep space objects and the furthest stars) making them dimmer is not a good idea if you want to be able to see them (and with increased detail).

Why High Magnification May Be Better

Taking the light of spacial objects into consideration, it is important to note that some objects are bright and emit a lot of lot.

This means that using higher magnifications would be preferable.

The planets of the Solar System are prime examples. High magnifications work best on Jupiter, Saturn, Mars, and other bright objects like the Moon.

The Right Magnification For You

By now, you will have learnt that each telescope comes with its own limits on magnification, and that eyepieces can effect it quite dramatically.

The right magnification for you will depend on the telescope that you are using and what you are hoping to observe.

Another thing that you will need to consider are the seeing conditions; you need to make sure that air turbulence is low, there is not too much cloud etc.

Remember more magnification is not always better; it does not necessarily provide a better view. Instead lower power almost always yields a better image.

All this being said, here are general rules for magnification when observing the night sky:

  • It is not ideal to push the magnification beyond 2x the diameter of your telescope in MM. So for a 3 inch telescope (converted to MM that is 75mm) x2 =150x magnification would be the max. Beyond 150x, even with ideal conditions your images of the sky will be large but blurry.
  • Air turbulence limits how much you should magnify further and larger telescopes are more affected.
  • Telescope magnification varies tremendously with time, location and season. 12″ Dobsonian, that can reach 600x Magnification on a good day, can be limited down to 150x.

Now, if you have average conditions and are using a standard-size telescope (Refractors with a 3/4″ Aperture or a Reflector that is 6″ or bigger), here are some recommendations:

Jupiter is best seen just under mid-high magnification. You will not likely need beyond 200x magnification. This is because Jupiter has a low contrast and adding more magnification reduces this contrast which makes your view of it worse.

Saturn is better seen on a higher magnification, slightly more than Jupiter. Typically 200-250x magnification. Consider what you are trying to see, the planets atmosphere/the rings etc. The more detail you want to see increase the magnification.

Mars and the Moon work best with the highest magnification possible for your scope and the viewing conditions. As Mars is a small planet, contrast is not as big of a factor that you need to consider so you can afford to increase the magnification.

Final Words

There is a lot more than meets the eye with what defines “Good Magnification”.

Ultimately What Is a Good Magnification For a Telescope is the balancing act and compromise between the size and the blurriness.

If you are looking for the best telescopes for observing the night sky; that factor in magnification and provide you with all the eyepieces you need, then read this.