When you’re using an auto setting on your camera, the camera will use its metering system to determine the appropriate depth-of-field for the photograph you are currently composing. However, using a manual setting allows you to control depth-of-field yourself, thus allowing you much more creative options in your work – if you understand the principles properly.
The type of camera you work with will effect how much control you have over your depth-of-field, as well. Most compact and point-and-shoot cameras do not allow you to set your own focal points, thus limiting your ability to control where your focus ends up. This can be extremely frustrating when shooting an object up-close, when you want to really narrow in on your subject. Narrowing your focusing options consequently limits your control on depth-of-field, so SLR cameras are preferable when possible. They allow you maximum, manual control and provide you with many more options than a camera that’s compact.
Three factors (besides camera choice) determine depth of field: your camera’s lens aperture, your lens focal length, and your focusing distance. Each factor will be discussed in turn.
Lens Aperture Setting: To say that a photograph has a deep depth-of-field is to say that much, if not all, of the photograph will be in sharp focus. Conversely, setting a shallow depth-of-field causes very little of your photograph to be in focus. Setting a deep or shallow depth-of-field depends on you and the goals you are aiming for. A small aperture, such as f/16 or f/22, gives a very deep depth of field, while a wide aperture such as f/2.8 or f/4 gives a very shallow depth-of-field. SLR cameras often have a setting known as AV, or Aperture Priority, which allows you to set the aperture yourself while the camera determines the shutter speed for you. I recommend this setting for those who are still trying to get the hang of manual exposure.
Lens Focal Length: As you increase your focal length, you reduce your depth-of-field. Vice versa, a very short focal length equals a very deep depth-of-field. A wide-angle lens, at 22mm, set to an aperture of f/22 will give you a much deeper depth-of-field than a 200mm telephoto lens set to the same aperture. Keep in mind what type of lens you’re using and how that will effect your end results.
Focusing Distance: The further away you are from your subject, the greater your depth-of-field will be. On the same note, the closer you stand to your subject, the more your depth-of-field will decrease. Say you are standing in front of a sign, around two feet away. If you photograph the sign at f/4 from four feet away, your depth of field will be very shallow. However, if you photograph the same sign from, say, thirty feet away at f/4, your depth-of-field will increase.
Try to picture in your head what you want your photo to look like in its finality, and then set your aperture to the f/stop which will best give you your desired result. Understanding depth-of-field will take practice and cannot be mastered overnight, but continuously working at it by using manual settings to maximize your options will hone your skills. As with most other photographic techniques, you will only improve if you make the effort.