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Aperture is one of the fundamental elements of photography. Photography is the capturing of light hitting a subject in your viewfinder.

I know that is the least creative way to explain this art form, but for the sake of this article, it is true.

The other two elements used to capture light are shutter speed and ISO. These three pillars make up the Exposure Triangle (seen under heading Setting Aperture).

Aperture might be the single most important tool in the world of photography, as it has many uses.

It can blur backgrounds and allows you to manipulate the amount of light the photograph soaks up. Here, we will go through everything you need to know about what it is and its uses.

What Is Aperture?

It’s a diaphragm in your lens that lets light hit your camera film or digital sensor. The bigger the hole, the more light can enter, and vice versa.

This element is also known as f/stop, where the f stands for ‘full’. Typical ranges used in photography start around f/1.4 and go up to f/22.

When you think of this opening and closing of the lens, it might help to think of your own eye. In this concept, your iris is your lens and can expand or contract your pupil, which is the aperture.

The iris changes due to the amount of light you confront. The more light, the smaller your pupil goes. Basically, it gets smaller as your eyes need less light to see the objects in your vision.

The technical definition of aperture is: “The opening in a lens through which light passes to enter the camera.”

Effects of Aperture

It has two main uses. It controls the light through exposure and determines how much of your view is in focus through depth of field. Here we will go through these terms.

Exposure

One of the two important effects the aperture has is to control the brightness of a subject. Here, the brightness is called exposure. How well your image is exposed comes down to how much light is let through the aperture.

A smaller aperture such as f/2.8 lets in a minimal amount of light, and will make the image darker.  In opposition, a wider one, such as f/22 lets in much more light and makes your image brighter.

A photograph of a bridge showing the difference of exposure from changing apertureWhen it comes to photographing in low light conditions, a wide or large aperture would work best. This lets in as much light in as possible. The complication is that f/2.8 is referred to as a wide or large aperture, even though the number is small. F/22 comparatively is considered small.

Depth of Field

Depth of Field is the other main reason why we use aperture. The depth of field refers to how much of your image, or subject is in focus. A small or ‘shallow’ depth of field is a small focal area, where the background would be out of focus. A large or ‘deep’ depth of field is where the whole image is clear and focused, subject and background.

F/stop

The f/stop is another term for aperture. We use f/stop as our cameras, digital or analogue, show the values in terms of ‘stops’. The values can be seen as F/8, but on digital camera LCD screens, they omit the slash and show only F8. As you can see here, the f/stop is shown as F2.8. This is a shallow depth of field and a wide aperture.

We use f/stops to describe how open the aperture is. If someone told you they had taken their photograph using f/22, you know that would be a small aperture giving a deep depth of field.

A Canon camera LCD screen showing F2.8, a wide aperture

Size of Aperture

As mentioned before, these values and terms can become confusing. Lenses that stop down to f/1.8 has a larger aperture than a lens that stops at f/2.8. This is confusing as when we think of larger, we think of a bigger number. Here, it works in reverse.

A diagram showing all sizes of aperture.

One thing that might help you understand this better is knowing that apertures are fractions. An f-stop of f/8 becomes the fraction 1/8th. This fraction is much smaller than the fraction 1/2 (f/2).

When you see photographs with a large aperture, they were taken using f/1.4, f/2 or f/2.8. Photographs with a small one will use something like f/16 or f/22.

See the following example to show the size of the aperture in comparison to their photographs.

An image showing the aperture size and the relative images taken

Choosing the Correct Aperture

Let’s have a look at a few exposure examples.

Having a wider aperture means more light can enter the lens and hit the film or digital sensor. F/2 will let in much more light than f/22. Have a look at this following example on what lighting each f/stop will give you of the same scene.

An image showing the respective depth of field and exposure due to aperture change

The first thing to note is that there are no rules when it comes to choosing an f/stop It depends greatly on whether you are going for artistic effect or to accurately reproduce a scene in a photo.

Setting Aperture

The three elements of photography are Aperture, Shutter Speed and ISO. By looking at the exposure triangle, we see that all three work on the amount of light allowed to hit the film or digital sensor. All three work co-dependently.

If you were photographing a scene at f/8 with a shutter speed of 1/250 and an ISO of 200 and wanted to get a shallower depth of field, you need to change the f/stop. As the aperture becomes bigger, to f/2.8, it will let in more available light. The image gets brighter. To keep the same, correct exposure, one or both of the other two elements needs to change to compensate.

As moving from f/8 to f/2.8, you need to go through three full aperture stops (f/5.6, f/4 and f2.8). This means your image will have three exposure values above correct exposure (+3EV). This means that these 3 exposure values need to be taken out of the other two elements, namely shutter speed and ISO.

As the ISO can typically only go to ISO 100, that is one stop. So, the light needs to be taken out of the shutter speed. The shutter speed will have to change to 3 stops darker. Shutter speed will go from 1/200 to 1/1600 (1/500, 1/1000 and 1/2000). So the new values will be F/2.8, SS 1/2000 and ISO 200 (or F/2.8, SS 1/1000 and ISO 100).

The great thing about these three elements is that if you move one element up to make the image lighter, you will need to move one of the two elements down. This compensates and rebalances to achieve correct light exposure. This will only work if the available light hasn’t changed. If the did change, then you will not need to compensate by making the image lighter.

A diagram showing the exposure triangle, looking at ISO, shutter speed and aperture.

Aperture Priority

We always recommend setting the aperture manually, which you can do using aperture priority (A/Av) or manual (M) mode. These can be set from your settings menu on your cameras LCD screen, or by using a dial on the top of your cameras’ body.

With aperture mode, you are free to set it as you see fit, and the shutter speed will change automatically.

In manual mode, you will need to change everything yourself.

An aerial view of a Canon DSLR, pointing out the aperture priority controlLens Possibilities and Limitations

Every lens has a limit on the largest, achievable aperture. Lenses are described by giving you all the information you need. Their system, their focal length and the largest aperture is all in the name of the lens . For example, Canon EF 24-70mm f/2.8L tells us it is made by Canon, for their EF digital system cameras and has a 24-70mm focal length. The largest it can go is f/2.8.

Smallest achievable apertures are not so important as all modern lenses will go to f/16.  This is more than enough for keeping most of the scene, if not all, in focus.

Some zoom lenses have a variable aperture, such as the Canon EF-S 18-55mm f/3.5-5.6. The largest aperture shifts from f/3.5 at it’s widest end to f/5.6 at the longer focal lengths. Expensive zoom lenses tend to have a consistent largest aperture throughout its zoom range.

The construction of prime lenses, due to the lack of mechanics inside, means they tend to have bigger apertures. These are great lenses for low light and some can reach f/1.4 or even f/1.2.

For more information concerning zoom and prime lenses, have a look at our article here.

Canon 24-70 f/2.8 zoom lens as an example for showing a maximum aperture

Conclusion

Aperture is a very crucial part of photography. Apart from controlling the amount of light, it also determines the depth of field. Both of these tools affect the image in such a huge way.

Imagine not being able to single out one person in a huge crowd. Or photographing an insect on a leaf, focusing on just the insects head. The world of photography would be a bland place without depth of field.

You will find that you will change the aperture more than anything. The only thing it cant do is utilise movement, which is the job of the shutter speed.

Aperture is one of the most basic yet important aspects of photography. You can’t hope to improve if you do not have a basic level of understanding, on what it can and cant do. The best way to learn, it to get out there and practise for yourself.

One thing worth mentioning is that the largest aperture is rarely the sharpest f/stop. You will find that if your lens does indeed drop down to f/1.4, your sharpest images will be taken two f/stops smaller. This will be f/2 (f/1.8 and f/2).

Photographing a subject with a wide aperture will be difficult if the subject is moving. An example would be using f/2 to photograph musicians during a live concert. As they move, that small focal length you placed on their eyes will move.

Use a smaller aperture to make sure you capture the image, by using f/2.8 or f/4 instead. You can still create a blurred effect on the image in post-processing.

A note from Josh, ExpertPhotography's Photographer-In-Chief:

Thank you for reading...

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Craig Hull

Craig is a photographer originally from the West Midlands (go Led Zeppelin and Black Sabbath) currently based in Budapest. There isn't much photography he hasn't tried, but his favourite photographic areas are street and documentary photography. Show him a darkroom and he'll be happy in there for days. As long as there are music and snacks. Find him at craighullphotography.co.uk and Instagram/craighullphoto

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