If you’ve read anything about photography before now, you may have come across the term ‘shallow depth of field’ or even just references to ‘depth of field’ - which can be a confusing term, unless you know what is meant by ‘field’ in this context.
So what we’re talking about here is your entire ‘field of view’ - or more specifically, the space between your camera and the furthest point you can see in front of you.
Think of this entire distance as being like a loaf of sliced bread, and within it, you have ‘slices’ of focus. You can choose to have just one slice in focus, some of them, or all of them. When you only have one or two in focus, this is known as ‘shallow depth of field’ and will result in a blurry background behind a sharp foreground subject.
To choose the number of slices that you want in focus, you need to change your aperture. A big hole (wide aperture – f3.5 or wider) will give you just one slice in focus, whereas a small hole (narrow aperture – f22) will give you all the slices in focus, from where you are, to as far as you can see.
This works on a sliding scale from one extreme to the other. So in between these two extremes is a medium aperture, which gives you some, but not all, of the slices in focus.
An easy way to remember it is that f3.5 is 3.5 slices of bread in focus (‘shallow’ depth of field) and f22 is 22 slices of bread in focus (‘deep’ depth of field). That’s just a rough approximation of course, but it gives you an idea!
The transition from sharp to blurry is gradual, so where you have a row of items you will see a gradual change in the amount of blur – but where you have a subject standing in front of a distant background, the subject will be sharp and the background will be blurry.
Going back to the loaf of bread analogy, it’s also important to note that the slices of focus near the camera are thinner than the ones in the distance, so the effect of shallow depth of field is more noticeable on subjects that are close to the camera. This is why it’s much harder to get a blurry background on a subject that is further away.
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