Aperture and Depth of Field

Discovering North Yorkshire through Photography and Video

Aperture and Depth of Field is very important to understand if you are determined to learn photography. The reason why it is vital to understand depth of field is because it can have a huge impact on the sharpness of your image. It also involves how you capture space and depth in a way that looks eye-pleasing and creative. Understanding depth of field will assist you as a photographer to produce some stunning photographs.

Aperture Values

Aperture and Depth of Field

Aperture and Depth of Field is measured in stops known as f stops (sometimes referred to as f numbers). When your camera is in Aperture Priority mode or even Manual mode, you will need to adjust the f-stop value to suit the scene. In a landscape shot, you will notice that the image is sharp throughout. However, a close up of a flower head for example, will most likely have a blurred background and a sharp subject. A sharp image throughout the scene is known as a Deep Depth of Field. Our flower head on the other hand, because the background is blurred, is referred to as a Shallow Depth of Field. So how do we as a photographer attain a deep depth of field or a shallow depth of field?

Deep Depth of Field (Sharp Throughout)

Aperture and Depth of Field

As mentioned, a deep depth of field is a scene that you want to present sharp throughout such as in a landscape for instance. To attain this, you will need to understand f-stop settings. The higher the number in the f-stop, the more of your photo is going to be presented sharp. Do not be mistaken for assuming that the f-stop number represents the width of the aperture itself. The number actually corresponds to the size of focus area in your shot. Depending on how much light you have, you will need to use a minimum of f8 above to have a sharp image throughout. If the scene is really bright, you can attain a high f-stop number such as f-16 and above. If the sun is in your shot it is recommended to go even higher. A very high f-number will return the sun in a star shape effect. The same is true in night shots of street lights for example. Of course, you need to be mindful that if you use a high f-stop number in low light, you are going to need a timer/remote and a tripod. This is because the shutter duration will extend and compensate for the lack of light, causing motion blur if handheld.

This image was taken with a F16 aperture rendering the scene sharp throughout.
Aperture and Depth of Field: This image was taken using an f-stop of f16, rendering the image sharp throughout the scene.
Aperture and Depth of Field: This image was taken using a f4.5 f-stop value which doe not appear as sharp.
Aperture and Depth of Field: This image was taken using a f4.5 f-stop value which doe not appear as sharp.

Another point to remember is that a smaller focal length also assists to produce a sharp image throughout. This is why not extending the lens right out to its full extent is preferable in landscape scenarios. The less magnification the sharper the appearance will be throughout.

Shallow Depth of Field (Blurred Background)

Aperture and Depth of Field

Using a shallow depth of field can be a simple way of returning an eye-catching subject. We mentioned that a high f-stop will return a sharp image throughout, but with a shallow depth of field, we need to reduce the focus area using a low f-stop position. You can also extend your lens right out to its full extent to capture a sharp subject and at the same time blur the background. Going back to our flower head scene, you will want to focus particularly on the centre of the flower so that it is complete sharp in your shot. The same principle can be applied to portraits where you would focus on the eyes.

Aperture and Depth of Field: This image was taken by extending the lens to its fullest. This has focused on the fence post and blurred the background behind it.
Aperture and Depth of Field: This image was taken by extending the lens to its fullest. This has focused on the fence post and blurred the background behind it.
Aperture and Depth of Field: This image was taken by retracting the lens to its fullest. This has focused on the fence post and although some blur exists behind the subject, it is nowhere near to the same extent as the first image above.

Again, you might be mislead into believing that the f-stop number corresponds to the size of the aperture, but in fact it is the size of the focus area. In this scenario we are desirous of a smaller focus area in which case we need a smaller f-stop. However, if you look inside your lens, you will notice that the aperture is very wide. On the flip side of the coin, if you set your aperture value to f22 you will see that the aperture inside the lens is very narrow. This might be opposite to what you might expect, so why is this?

Understanding Aperture and Depth of Field

Aperture and Depth of Field

The best way to explain why a wider aperture produces a blurred background and a narrow aperture produces a sharper image throughout is to show you. This image reveals how the sharp focus area identified in blue is regulated by the aperture size. When the aperture is made smaller, the field of view is also smaller in the background creating a sharper image. With a wide aperture, the background view is also extended and this is out of focus, identified in red.

A pinhole aperture would narrow the rays of light, more technically known as collimated, keeping a sharp image throughout the shot.

On the opposite end of the scale, a wide aperture would allow in more light, but only the light collimated would be in focus, that being on your subject you have focused on. The light that isn’t collimated would not be focused and will result in blur.

All you need to understand is that f2.8 is a wide aperture resulting in background blur (a shallow depth of field) and an f22 would result in a sharp background ( a deep depth of field). The number in f stops are pertaining to the size of focus area, not the size of the aperture itself.

Why a narrow aperture creates a sharper image throughout and a wider aperture blurs the background.
Aperture and Depth of Field: You may be bemused as to why a wide aperture would create a blurred background or a shallow depth of field and why a small aperture would create a sharp scene throughout or deep depth of field. It is simply owing to the rays of light and their direction. A pinhole aperture would narrow the rays of light, more technically known as collimated, keeping a sharp image throughout the image.
On the opposite end of the scale, a wide aperture would allow in more light, but only the light collimated would be in focus, that being on your subject you have focused on. The light that isn’t collimated would not be focused and will result in blur.

Also, imagine if you extend your lens right out to it’s full extent and you focus on your subject. The background will be rendered out of focus, yet your subject will remain sharp. The direction of light will be changed as a result, bringing in more of the out of focus area.

If you have a long lens for your camera, go outside and have a practice. Notice what happens when you take landscape or streetscape shots with both a low f-stop and a high f-stop. Now try extending your lens right out and take a photo of an object. What happens to the background?

Points to Remember

Aperture and Depth of Field

  • To attain a sharper image throughout you should use less magnification, use a high f-stop and a shorter focal length.
  • To attain a blurred background, focus on the part of the subject you want in crips focus and either use a low f-stop and/or extend your lens right out.

Key Camera Skills

Camera Shutter Settings

Aperture Value and Depth of Field

Image Quality Settings

Mastering Colour Settings

Photo Sharpness

Thornton le Dale to Low Dalby Walking Route