We’ve talked a lot on this site about aperture and how it affects depth of field, but not a lot about depth of field itself. Understanding depth of field can help you learn how to create really compelling portraits of your kids, family, and others – even photos of food, pets, and bugs. So let’s get started:
Depth of Field: What is it?
In the most basic of terms, depth of field (sometimes noted as DoF) is how much of your image is in focus, from front to back. If just your focal point is in focus (such as your child’s face) then this would be shallow depth of field, not much in focus. If a lot of your image is in focus, such as with a landscape, this would be large depth of field.
Controlling Depth of Field
Aperture is your primary method of controlling depth of field. Choosing the widest aperture your lens offers (you’ll see it stamped on the front of your lens, such as f/1.8, f/4 or f/5.6) will give you shallow depth of field (i.e. fuzziness). A narrow aperture (such as f/16 or f/22) will give you a larger depth of field.
If it helps, a bigger number after the “f” = more focus.
How far you are from your subject affects your depth of field also – the closer they are to the camera (as in, the farther they are from the background), the shallower the depths of field will be, so the focus will be more on your subject and less on the background.
How Lens Length Affect Depth of Field
No matter how wide your maximum aperture is, the length of your lens can affect on depth of field. In simple terms, an aperture of f/4 on a 70mm lens will not give you the same depth of field as f/4 on a 200mm lens, assuming you are standing in the same location to take your photo, as the 200mm will get you much closer to your subject for a shallower depth of field. However, if you get close to your subject with a wider lens you can imitate the same effect.
When it comes to lenses, a fixed focal length lens (like 50mm) will offer wider aperture for a better cost than a longer or zoom lens (i.e. 75-200mm).
Using Depth of Field
A shallow depth of field can help to make certain parts of your image stand out. For kids portraits this will most often be the face, especially the eyes – but not always. Sometimes a hand, foot, ear, or other part of the picture can be the primary point of focus to create an interesting image.
Give it a try. Start at f/5.6 in Av mode (so you can control your aperture) and work up or down, using different points of focus and changing your distance to your subject to create dynamic portraits of your kids.