A Beginner’s Guide To Magnification With Telescopes

If you’re new to astronomy or just want a refresher course on the basics of using telescopes for stargazing, this guide will help get you started with your first telescope.

Keep reading to discover our ultimate beginner’s guide to magnification with telescopes. 

A Beginner's Guide To Magnification With Telescopes

How Does A Telescope Work? 

The primary function of a telescope is to magnify an object to be seen through the eyepiece.

The size and quality of the telescope determines how much light is gathered by the objective lens (the front element), which determines how well objects are magnified. 

A good rule of thumb is that the larger the aperture (diameter) of the objective lens, the better the telescope’s performance.

However, other factors are involved, including the focal length of the objective lens, its distance from the eyepiece, and the type of eyepiece used.

There are two main types of telescope: refractors and reflectors. Refractors use lenses to focus the image onto the retina, while reflectors have mirrors instead.

Both types work very similarly, but they each have their own advantages and disadvantages.

For example, both types of telescope require more skill to operate than do binoculars, because they require precise alignment of the optical components.

This means that beginners should start out with binoculars before moving up to a telescope.

How To Magnify Objects With Your Telescope

To see something as small as a star requires a telescope with a large enough aperture (objective lens diameter). In general, the higher the power rating of the telescope, the greater the amount of light gathering ability.

Power ratings range from 10X (10x) up to 300X (300x). Most people start with 100-200X power, depending on what kind of viewing experience they wish to have.

As mentioned above, there are two main types of telescope: Reflector and Refractor. These terms refer to the shape of the glass elements inside the telescope.

Refractors use prisms to bend light into parallel rays, whereas reflectors use curved mirrors to direct light into parallel beams. Each type of telescope has its strengths and weaknesses, so we’ll discuss them separately below.

Understanding Telescope Magnification 

If you’ve ever looked at an object through someone else’s telescope, you’ve probably asked the question, “what magnification is that?”.

So it’s an important question to ask, and as astronomers, it’s important to be able to answer the question. 

Understanding Focal Length & Magnification 

Most amateur telescopes come equipped with either a fixed focal length or variable focal length.

Fixed focal length telescopes have a single focal length, meaning that the entire system focuses on the same spot regardless of where the observer moves the telescope. 

Variable focal length telescopes allow the user to change the telescope’s focal length, allowing for different views of the sky.

When observing the night sky, most people prefer using a variable focal length telescope since it allows them to move around without re-adjusting the scope.

The focal length of a telescope refers to the distance between the center of the objective lens and the point where the image appears when viewed through the eyepiece.

For example, if the focal length is 50mm, then the distance from the objective lens to the eyepiece is 50mm.

The focal length of a telescope is measured in millimeters. A typical focal length for a telescope is 200mm (8 inches).

Calculating Magnification

If you look through a telescope, there are two ways to calculate how much closer or farther away an object will appear. One method is called multiplying by the inverse square law.

Another method involves calculating the ratio of the object’s apparent size divided by the actual size of the object.

The first method is easier to understand, but the second method is often used by professionals who need to know exactly how far away an object appears.

Multiplication By The Inverse Square Law

To determine how close an object appears, multiply the focal length of your telescope by the inverse of the square of the distance between the object and the center of the objective lenses.

For example, if you were looking at a distant galaxy, 3 million light-years away, and your telescope had a focal length of 200mm, then the galaxy would appear 1/1,000th as big as it actually is.

This means that the galaxy would only appear about 0.01% as bright as it really is.

Ratio Method

To determine how far an object looks, divide the focal length of your scope by the diameter of the aperture of the eyepiece.

For instance, if you’re viewing a star through a 100mm refractor, the star would appear 10x larger than when seen with the naked eye.

How Do I Know How Much My Telescope Is Magnified?

This is a very common question among new amateurs. There are several methods to figure out what magnification your telescope has. The easiest way is to use the following formula:

Focal length of the scope ÷ focal length of the eyepiece.

To find out the focal length of the scope and your eyepiece, simply have a look around their enclosures. Their focal length should be labeled pretty clearly.

However, if you cannot see any markings, refer to your user manual or check the manufacturer’s website.

What Does It Mean When My Scope Says “Variable Focal Length”?

Most scopes sold today are variable focus scopes. These scopes have multiple focal lengths that can be changed by rotating the scope’s main tube.

It’s not that fixed focal length telescopes will only give you a singular focal length and thus one magnification, it’s that they work in large increments.

For example, you may have an eyepiece that offers both 10 and 25 mm focal length settings, but it can never be between those figures. It has to be one or the other.

With a variable focal length eyepiece, you can cycle smoothly, by degrees, from the minimum all the way through to the maximum focal length, giving you far more flexibility in terms of magnification.

What To Look For When Buying A Telescope

When buying a telescope, make sure you get one that is designed to suit your needs. For example, most telescopes come with various accessories such as eyepieces, finderscopes, collimators, etc.

If you want to buy a telescope, many different brands are available. Each brand has its own advantages and disadvantages. Before making your purchase, do some research online and read reviews written by other users.

If you plan to take pictures with your telescope, you should consider getting a camera tripod. A good tripod will help keep your camera steady while taking photos.

There are many different kinds of cameras for astronomy. Your best bet is to go to a store that sells telescopes and ask them for recommendations.

The most important thing to remember when using a telescope is safety. Make sure you know how to operate the controls before attempting to look at something.

For example, the image quality of a telescope depends on the size of the primary mirror, the number of secondary mirrors, the amount of glass used, and the quality of the optics.

The biggest advantage of a telescope is that it allows us to see things we couldn’t see without it. It lets us see objects that are too small or too dim to see with our eyes alone.

Final Thoughts

Astronomy is a great hobby! If you enjoy observing the stars, planets, galaxies, and nebulae, you’ll love learning about the universe. The sky above us is full of wonders waiting to be discovered.

All you need is a little knowledge and a lot of patience. Good luck exploring the cosmos!

Gordon Watts