The Compound Light Microscope – Optics, Magnification And Uses

The invention of microscopes brought a whole new aspect to scientific investigation. Essentially, a microscope is used to magnify really small objects, allowing us to see them as if they were enlarged and right up close to us. 

The Compound Light Microscope - Optics, Magnification And Uses

This has allowed us to study loads of the natural world and get a better understanding of how things work, such as organisms and even cells.

However, there are many different types of microscope available, such as the compound light microscope. But what does it do and how does it work?

Below, we have all the answers for you! If you read on, you’ll find out all about the compound microscope, from its optics to its magnification levels. On top of that, we’ll also delve into the many uses that it has. 

What Is A Compound Light Microscope?

First, let’s start with outlining the basics. A compound light microscope is a variation of microscope that has more than one lens to it, as well as its own light source included too. 

The different types of lenses that the compound microscope has each have different purposes. Traditionally with this type, it has ocular lenses and objective lenses. What do these each offer?

Well, the objective lens should be the one that gathers light from the thing being observed. This light is then focused to help produce the real image that you’re then seeing through the ocular lens. 

The lenses are placed in different positions to aid this passage of light and image. The objective lens is put in the rotating nosepiece of the microscope, where it is closer to the object you’re looking at.

On the other hand, the ocular lenses are in the binocular eyepieces. You can get one that has just one ocular lens, but typically the binocular microscopes are popular. Why are they preferred?

Well, having two eyepieces (binocular, think bi-oculars) eases your viewing, making the eye strain much more reduced than with one eyepiece.

What Is A Compound Light Microscope?

Why is it called a “light” microscope, though? As we’ve suggested, the microscope has its own light source.

This should be an incandescent bulb, which lights your subjects from underneath so that you can look down on them from above. 

These microscopes come under the term of “bright field” microscopes, which are popular because they are the most simple range of illumination techniques.

With most final magnified images, you’ll know it’s a bright field microscope image because it’ll feature a dark sample on a bright background.

This contrast is really handy for scientists, because the samples and specimens are made much clearer when their surroundings are such a dramatically different shade.

How Do Other Microscopes Compare?

Let’s briefly look at what other types of microscopes there are, just so you know the difference – and understand why compound microscopes are sometimes used over other varieties. 

Stereo Microscopes

These offer a magnification somewhere between 10x and 40x, and usually allow both transmitted and reflected illuminations.

A key difference between stereo and compound microscopes, though, is the dimensions of their image.

Stereo microscopes allow the viewer to get a 3D image of their specimen, while compound microscopes only offer a 2D image.

But why is there this dimensional difference? Well, a microscope with lenses capable of as high a magnification as compound microscopes inevitably has a shallow depth of field and therefore gets pictures that are mostly out of focus.

As a result, we get a flat two dimensional image. 

Polarizing Microscopes 

These microscopes are unique in that they use a polarized light. In these types of light, the light waves are vibrating in one direction only, which is opposite to typical light waves, where the light vibrates in lots of different random directions.

You can get a polarizing microscope to be compound, but it doesn’t always have to be. 

When you’re looking at your objects, the light has to go through a polarizing filter to allow you to view it properly.

Sometimes this won’t be quite enough, though, and you’ll have to also pass it through an analyzer, which will improve the quality of the image’s contrast.

Polarizing Microscopes 

Inverted Microscopes

Compound microscopes are known as upright microscopes, which is where the source of the transmitted light is located below that stage, as is the condenser (a type of lens). Both of these point up to where you’ll be looking down.

Your specimens are placed on the stage, facing down. So what’s an inverted microscope? Well, it’s the opposite!

With the inverted microscopes, you are looking at your specimen samples from below. This is because the microscope’s optics are placed underneath the specimen and stage.

Why do people like to use the inverted ones over the upright? It can give the viewer greater working distance, with the room to move around. Additionally, it saves you time and money because only one side of your sample needs to be processed. 

Types Of Viewing Heads For Compound Light Microscopes

As we mentioned earlier, you can get compound microscopes with different numbers of eyepieces in them. Two eyepieces are the most popular because they reduce eye strain, but you can get all sorts. They are as follows:

Monocular / Single Eyepiece

These are the bottom end, giving only one eyepiece for you to look through. These tend to not offer as much magnification as microscopes with more eyepieces. However, there is a benefit: they’re cheaper! Also, they weigh much less too.

Monocular / Single Eyepiece

Binocular / Two Eyepieces

These are the most common, offering two eyepieces for you to use. This reduces eye strain, as well as offering more magnification than a single eyepiece would give you.

Trinocular / Three Eyepieces

This, with three eyepieces for you to use, is as high as it goes! The third eyepiece can come in the form of a tube that offers great alternative views: either somebody else can look through it, or a CCD (charge coupled device) camera can even operate through it.

This type of microscope certainly offers the most options, but it is more expensive than the others, and sometimes that extra eyepiece simply isn’t needed. 

Magnification Of Compound Light Microscopes

Let’s get back to the compound light microscope, and begin looking at its properties and qualities. 

Magnification is the process of making an image of an object much larger. Obviously you’re not making the object itself larger, but you are making your view of it much larger.

What are the benefits of this? Well, they’re pretty clear! 

If a specimen is too small, you can’t really get a good view of it, and you’re left unable to study with any meaningful amount of clarity and detail.

If you enlarge the image, on the other hand, then you’re making every part of it bigger and clearer. If a scientist is examining something crucial, like cells that are related to an illness or disease, then it’s crucial that they can see every part that makes it up.

It is this extra level of detail and information that enables scientists to properly use the world around us, understanding more and more each day.

So how good is the magnification that a compound light microscope offers, and how can you calculate it? On a general level, they should offer anywhere between 40 and 1000x.

These numbers refer to how much larger the image is than the original specimen. So, something that is being viewed on 1000x magnification is 1000 times larger than the actual original object.

This is an amazing level of enlargement!

The magnification of a compound microscope works by multiplying the magnification powers of the individual lenses. As we’ve said before, these will be the ocular lens and the objective lens.

Magnification Of Compound Light Microscopes

As you know, the ocular lens is also known as the eyepiece lens, because it’s the one that’s close to your eye, whereas the objective lens is the one that’s close to the specimen itself – remember it as objective as in close to the “object”!

Calculating the total magnification, then, will require some math.

The ocular eyepiece lens is often 10x, meaning that on its own it would give you an image just 10 times bigger than the original specimen. Alone, this wouldn’t be good enough in most cases!

So the objective lens on top of that is essential. Objective lenses work at either 4x, 10x, or 40x. Find out which you have in your microscope, and multiply it by the 10x of the ocular lens. 

Let’s go through an example, just so that you’re sure! Imagine our compound light microscope has the expected 10x eyepiece lens and a 10x objective lens.

If we multiply them together, we do a clean 10 times 10, which equals 100. This means that this microscope will make a total magnification of 100x, which means that the image will be 100 times larger than the specimen itself. 

For another example, let’s take the absolute top end. If we do 10x eyepiece times a 40x objective lens, we would calculate the total by doing 10 times 40. This gets us a result of 400!

This means that the total magnification of this compound light microscope is 400x, which – as you know – means that your magnified image of the specimen is going to be 400 times larger than its real life size.

Which is a pretty big difference! You’ll definitely be able to make out more detail.

Working Distance Of Compound Light Microscopes

Working distance doesn’t just mean the distance that you have to commute to your job! When regarding microscopy, working distance carries a whole new meaning.

Put simply, working distance is the distance between the tip of the microscope’s objective lens and the surface of your specimen (or, if you’re using a slide, then it’s the point where the specimen is in focus).  

An interesting correlation is that when you have low magnification, your working distance is going to be longer. On the other hand, when your magnification is higher, then your working distance is going to be shorter. 

You must be careful, though, not to get too close physically to your specimen. If you increase your magnification, you could knock your lens into the specimen slide itself and damage it.

Working Distance Of Compound Light Microscopes

Resolution Of Compound Light Microscopes

This is the ability that your microscope has at making out detail in your specimens – it’s the clearness of the image. That being said, the more you magnify an image won’t make it clearer.

Instead the images will just blur together. “Resolving power” is the term for when these close images can be distinguished apart. 

For compound microscopes, the wavelength of the light waves that are in play actually limit the resolution. The top end of compound microscopes can’t determine bits of a specimen that are closer together than roughly 200 nanometers. 

What Can I View?

As we’ve said, compound microscopes are part of the bright field family. These allow many different things to be viewed, in different conditions. 

For example, if you have a prepared and stained slide then you can see the following: bacteria, large protoists, thin sections with condensed chromosomes.

If you have slides with smears on, you can see: blood and negative stained bacterias.

And if you have a living preparation (a wet mount for moving organisms), you can see: pond water, algae, living protists or metazoans. 

What Are The Other Qualities Of A Compound Light Microscope?

On top of being able to view all of those different kinds of specimens, there are many other benefits to having a compound light microscope. 

Firstly, their detail is very impressive. This is because of the multiple lenses that they have, which multiply their own magnification qualities together to create an overall – increased – total magnification.

This can go up to very high numbers indeed, and offer a great amount of detail and enlargement in their images. 

The fact that they are also part of the bright field family means that they are not overly complicated with their lighting and illumination, which is a bonus too.

What Are The Other Qualities Of A Compound Light Microscope?

This easiness with using it extends into the fact that it makes your final images in contrasts of dark against bright, which makes it a lot easier to determine details in your picture. 

Compound microscopes are also quite small compared to some other variations of microscopes, which means that they’re easy to lift and move around.
Be careful though! These are still intricate and expensive scientific devices. 

Speaking of expensive, obviously you can get a range of compound light microscopes – for example, with more eyepieces.

You should also get something that’s sturdier, as well as objective lenses that are free of tension and condensers that give you options about what contrasts you have. 

However, you can certainly get a compound light microscope that is more than good enough for a regular price.

You don’t have to splash out on the fanciest one, rather get the one that has the selection of parts that will work best for whatever you’re going to be viewing. 

Final Thoughts

And there you have it! The compound light microscope is one of the most popular types of microscope available on the market, and you can see from our guide exactly why that is the case.

They are pretty lightweight and easy to move about, for one. Their magnification is also impressive, which is largely down to their inclusion of multiple lenses that multiply together to create an even greater magnification.

The fact that they are lit shouldn’t be ignored, either, helping to illuminate your findings in a crisp way!

Whichever version of the compound light microscope you go for, you’ll be more than satisfied with its image results and simple use! 

Jennifer Dawkins