5. Aperture & Depth of Field

Aperture is one of the six essential elements of photography. It controls both how much light your camera is able to record and also the depth of field. Depth of field (DoF) is an important compositional and creative element in any image, so it’s important to understand what it is and how to control it.

What is aperture?

As we discussed in Chapter 1, aperture refers to the opening through which light passes before hitting your camera’s sensor. By controlling the size of that opening, we can control how much light is recorded in an image as well as the depth of field.

The larger the aperture, the more light is recorded and the shallower the depth of field. With smaller apertures, less light is recorded and the depth of field is greater. Aperture is recorded in f-stops and is shown by the symbol ‘f’.

Large aperture vs small aperture

Aperture can be quite confusing at first, but it’s important to understand the difference between large and small apertures. The simplest way to remember it is: the lower the number, the larger the aperture. When referring to ‘large’ apertures, we are not referring to a large number value. Instead, we are referring to the aperture or exposure value. So, for example, f1.4 is a large aperture, while f22 is a small aperture.

Large aperture size = Smaller f-stop number = Shallower DoF

Small aperture size = Larger f-stop number = Deeper DoF

What is depth of field?

Depth of field is the sharpness range either side of a focus point. This is controlled by the aperture. Larger apertures (smaller f-stop numbers) result in a shallower depth of field, where less is sharp. Smaller apertures (higher f-stop numbers) result in a greater depth of field, where more is sharp.

How to control depth of field

There are three different factors that influence depth of field — aperture, distance from your subject and magnification. First, let’s look at how to change your depth of field using different aperture settings.

If you’re shooting in Auto mode, your camera will decide the ‘best’ aperture for you. If you’re shooting in Aperture Priority mode, you can simply set the aperture by using your camera’s control dial and your camera will automatically determine the shutter speed.

If you’re shooting in Manual mode, you have the greatest level of creative control, but you have to balance your aperture and shutter speed to get the best exposure. In any of these modes, you can simply adjust your aperture using either the front or back control wheel of your camera.

DoF is also dependent on the distance from your subject. The closer you are to the subject, the shallower your depth of field will be. Shooting from further away will give a much greater depth of field. This is due to magnification.

Magnification can refer to the sensor size, focal length and distance from the subject. For example, a larger sensor size, longer focal length or closer focusing distance will result in shallower depth of field. At the same aperture, full-frame cameras will have a shallower depth of field compared to crop-sensor cameras. Again, at the same aperture, medium-format cameras will have an even shallower depth of field than full frame cameras.

Lenses and depth of field

Another factor in depth of field is your choice of lens. Different lenses have different depth of field characteristics, which is caused by the magnification of the lens. The greater the magnification (as with telephoto lenses), the shallower the depth of field, and vice versa.

This means that if you’re shooting at f4 using a 24mm focal length 10m from your subject, you will have much greater depth of field than if you were shooting f4 using a 200mm focal length at a distance of 10m.

Depth of field examples

This natural-light portrait image below was captured using an aperture of f1.2, keeping the subject sharp while the foreground and background remain out of focus.

Full open apertures, as used in the image above, are great for photographing people. Why? Because they allow us to blur the background and bring attention to the eyes or face of the subject. On the other hand, if we’re photographing landscapes, generally we want more depth of field so that we can see into the distance. This is why smaller apertures (such as f16) are often best for landscape photography.

An aperture of f22 was used for the image above. You can see how the depth of field runs much further, keeping both model and the background in sharp focus.

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Class 5: Aperture & Depth of Field