Depth of field is an important concept in photography, and one that is often misunderstood. Simply put, Depth of field (DOF) is the distance between the closest 'in focus' object in the photo and the farthest. A shallow depth of field will only have a small area around the subject in focus. A deep depth of field may have the entire photo in sharp focus.
Why Depth of Field Is Important
Depth of field determines the amount of the picture around the subject that is in focus. Controlling DOF controls what the observer sees in the photo. You can have deep DOF showing a panoramic view of the mountains, or a shallow DPF focused in the area around the tree with the hornet’s nest in front of those mountains. The reasons for manipulating depth of field range from having as much of a picture in focus as possible, making sure things you don't want noticed are obscured if you either can’t or don’t want to get them out of the frame.
How It Works
Several things affect DOF, but there are three that are relatively easy for the photographer to control:
- Aperture: Controls the amount of light reaching the sensor
- Focal Length: The distance from the lens to the sensor
- Focused Distance: The distance from the camera to the subject
Aperture is controlled by changing the size of the hole (the aperture) that light from the lens goes through to reach the camera sensor. Aperture settings are called f-stop and noted as the letter ‘f’ and a number. The higher the number, the smaller the aperture. So a setting of f2.8 is a large aperture that allows large amounts of light to reach the sensor. A setting of f11 is a smaller aperture that allows less light to reach the sensor.
As long as the other two factors remain the same, smaller f-stops provide deeper DOF larger f-stops provide shallower DOF.NOTE: Some compact cameras have the ability to adjust the aperture, but because of the size of the sensor, compact cameras may not reach extremely shallow DOF no matter what the setting.
Focal length is most easily controlled by changing the lens on the camera. On a compact camera focal length is usually fixed, or can only be slightly changed. Focal length is slightly controversial right now. Some experts say that focal length does not affect DOF. If conventional wisdom is correct, longer focal length means shallower depth of field. If the new theory is correct, depth of field is not affected by focal length.
Focus distance is changed by moving closer to, or farther from, the subject. The closer you are to the subject of your photo, the shallower the DOF. That is why landscapes, pictures of sporting events taken from the stands, and other photos taken from a distance have most, if not all, of the picture in sharp focus. Macro photos, on the other hand, are shot from very close distances. The depth of focus is very shallow, sometimes barely keeping the subject in focus.
Putting It Together
How you control depth of field depends on your equipment and the subject of your photo. If you have a compact camera that automatically selects aperture. You have to trick the camera into selecting the f-stop you want.
For a shallow depth of field you need lower light so the camera will choose a lower f-stop. Because of the smaller sensor they use, compact cameras tend to shoot with deep DOF, so won’t usually have to worry about those shots.
With a DSLR you can set your aperture. For shallow DOF set a low f-stop – 2.8 or 5.6, and shoot from as close as reasonable. For a deep DOF do exactly the opposite. High f-stop – f16 or higher, and from as far away as reasonable.
It is important to understand depth of field and how it works. Even if you have a compact camera with a fixed lens, if you understand how depth of field works you can manipulate your shots to increase decrease DOF, even if what you can do is limited. With a DSLR that allows much more control you can create magic through your lens.
Now that you know a little about depth of field, go practice and find your own methods and tricks to master it.