What is depth of field?

Depth of field is essentially how much of your image (i.e. distance in a scene) that appears sharp from the closest object to your camera up to the thing that is furthest away.

There are three main factors that influence your depth of field:
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- Your focus distance from your subject
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- The focal length of your lens
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- Most importantly, your aperture or f/stop

In addition to these, things like camera sensor size and even how a photo is printed can also influence what our eyes perceive as an acceptable level of sharpness.

It also important to know that there isn’t a sudden change in sharpness within your depth of field. In other words, there will be a gradual change from sharp to unsharp within the photo (a term known as the “circle of confusion”).

The reason that this is important, is because it can be difficult to spot when looking at your photos on the LCD screen on the back of your camera. You may only notice it when viewing the image in a larger size on a monitor.

This is why it is important to understand depth of field and use it correctly in your photos.

What influences depth of field?

As mentioned above there are various factors that influence the depth of field in your photo. So, it is important to understand some of the basics of these so that you can utilise depth of field correctly and effectively in your photos.
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- Aperture  

When most photographers refer to depth of field, this is often what they think of. It is with good reason as the aperture on your lens has a big influence on the depth of field within your photo. The aperture works in a similar way to our pupils in that the bigger it is, the more light it allows into the camera.

Where aperture can get a little confusing is in selecting the right one for what you want to achieve. As a wide or large aperture is actually selected with a low f/stop number and it gives you a shallow depth of field. While a small or narrow aperture is selected with a large f/stop number for greater depth of field.
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So just to be clear…

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Low f/stop = wide or large aperture which means shallower (or shorter) depth of field so only a smaller distance within your photo will be sharp
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Large f/stop = small or narrow aperture which means greater (or longer) depth of field so a greater distance within your scene will be sharp.

- Distance

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‍Now, it might be tempting to think that you can simply select a large f/stop (a small aperture) and ensure everything in your scene will always be sharp. Unfortunately, it’s not as simple as that as the distance between your camera and the subject also has an impact on the depth of field. A good example of this is if you have ever tried to take a close-up photo of something but even with a small aperture cannot get the entire object or scene in focus.

So, it is also important to know that the closer your camera is to the subject you are photographing, the shallower your depth of field becomes. In other words, if you want to extend that depth of field you need to move further away from your subject.

- Lens focal length

The third thing that you need to be aware of when it comes to depth of field is the focal length of your lens (i.e. how much you are zooming into the scene). This can be complicated to understand but as a rough guide, the longer your focal length is the shallower your depth of field becomes.

For example, imagine you are taking a photo using a 35 mm (full frame) camera at an aperture of f/4 of an object 5 meters away. At a focal length of 50mm the total depth of field (distance that would be an acceptable level of sharpness) will be 2.71m. Compare this to using a 100mm focal length and now your total depth of field will be 0.63m. Even though you are the same distance away and using the same aperture, your depth of field is shallower due to your focal length.
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Top tip:

There are plenty of great apps that calculate this total depth of field. Download on on your phone and if you're unsure, refer to it before taking a photo.

Why is depth of field important in photography?

Aperture (which controls your depth of field) together with shutter speed and ISO combine to form the "exposure triangle".

These are the three main settings that determine how a photo will be captured. Your depth of field is an essential part of this in helping you be able to take the photos that you want to make.

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Sometimes, you have no choice but to select a wide aperture to be able to allow more light to enter the camera - so that you can take a photo without using a tripod. At other times, you may choose to use a wide aperture for more creative reasons like wanting to blur the background in a portrait.

Either way, by understanding how depth of field works you will have more control over the photos that you take.

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How to select or change depth of field

To adjust your depth of field (without physically moving or changing lenses), look for the setting in your camera that changes the f/stop number. Keep in mind that whichever dial, or wheel changes the aperture might change depending on which mode (i.e. aperture priority, shutter priority, manual etc) you have selected. When you see a number with “F” before it moving, you know that’s what you are looking for.

Try to practice in selecting and changing the aperture quickly while you are looking through the viewfinder. The last thing that you will want to be doing is spending precious seconds trying to select the right thing when you have a fleeting moment in front of you.
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How to use depth of field more creatively

The great thing about depth of field is that it gives you an extra form of creativity. For example, selecting a very shallow depth of field when photographing objects or people can blur the background and make them stand out more. Or you can even take this further and use it creatively by for example focusing on a building with a shallow depth of field thus blurring the surroundings. Just be very careful to ensure that you are focusing on the right element in the photo when using a shallow depth of field.

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Conclusion

The examples in this article are just some of the uses of aperture or depth of field in photography. To gain an understanding of depth of field is an essential part of your photography journey and is something that will help you capture better images.

This beginners guide should get you started in understanding it... But the best way to really learn is to practice and experiment. So, get out there are start taking photos!

All images from Kav Dadfar.