There are several situations where controlling depth of field is important. The most common is portrait photography. As I mentioned at the start, portraits shot on an automatic camera using a medium aperture usually have a lot of sharp foreground and background detail, which can distract attention away from the main subject.
As you can see in this shot, which was taken using an aperture of f22, the model is in focus, but so is the background, which unfortunately makes it look like she has a tree growing out of the top of head.
By increasing the aperture to f5.6, we can make sure that only the subject is in focus. A blurred background is much less distracting, and the distance between the subject and the background is far more apparent.
Another situation in which depth of field is an important issue is landscape photography. Here it is often important to get the maximum depth of field possible, so it is usual to use the smallest possible aperture. This shot was taken using and aperture of f22, to ensure that both the foreground and distant background are in focus.
Focal length and depth of field
The focal length of your lens, in other words how much you zoom in on your subject, also has a large effect on depth of field. Generally short focal lengths (wide-angle settings) have much greater depth of field than longer focal lengths. This is one reason why, when taking a portrait shot, itâ€™s a good idea to step back a bit and zoom in rather than using a wide angle lens up close. Iâ€™ll cover this in more depth in my next tutorial.
This is a specialised technique of landscape photography which involves manually focusing the camera to the closest point where the depth of field makes everything in the shot sharp. Again, Iâ€™ll cover this topic in more detail in a future tutorial.