Depth of Field 101

Understanding and manipulating depth of field in an image is a key skill of professional photographers. A firm grasp on this concept can improve the quality of your work and can provide you with countless alternative ways to shoot one subject. Although depth of field may seem confusing, with a little practice it will quickly become second nature.

Depth of Field Defined

In a photograph, depth of field can be thought of as how "deep" the focus of an image goes. In more simple terms, the depth of field refers to the difference between the items in the background losing clarity compared to the subject in focus. Think of depth of field as the relationship between the focused and blurry elements of your photograph.

As an example, a flower with a blurry background and a sharply focused flower have a low depth of field while a landscape picture with everything in focus has a high depth of field. In either of those examples, changing the depth of field would have a dramatic impact on what the viewer experiences when looking at the final image.

What Influences Depth of Field?

One of the primary influences of depth of field is the length of your exposure. The longer a frame of film or digital sensor has to absorb the scene it is being exposed to, the greater amount of detail it will be able to accurately reproduce. Longer exposures will always result in greater depth of field, even if at unperceivable levels.

When it comes to changing depth of field, you can control it by increasing or decreasing the exposure time. You can do this by changing the shutter speed of your camera; slow speeds (60 and lower) will cause longer exposures and greater depth, while fast speeds (125 and higher) will decrease exposure times and cause the opposite.

How to Control Depth of Field

You can purposefully force greater depth of field into an image, however this will require manually adjusting the aperture settings of your camera. Since a long shutter speed is needed to add depth of field, a smaller amount of light will be let into the lens. If you increase your exposure but forget to close down your camera aperture, you'll end up with images that are over exposed.

Changing the aperture involves moving the f-stop (often the ring around the lens behind the focus ring) to whatever number lets in the best amount of light. Any new camera will let you pick a shutter speed and then will automatically adjust the f stop, but with older cameras, you'll have to play around with the light meter until the shutter speed syncs with the right aperture setting.

Helpful Tip: If you're working with high depth of field images it's likely that you'll be working with very long exposure times (depending upon the quality of your light). Shots of this nature will almost always require a tripod to prevent blurring from camera-shake.

In every picture you take, you should consider using depth of field as it's a powerful tool in your photographer's toolbox. Objects in a photograph all lend themselves to the story that image is trying to tell - what is and isn't in focus can mean quite a lot to the relationships between those objects. If you think about how depth of field could impact your pictures, you'll notice your images are much more interesting and powerful.