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. A good way to think of depth of field is that it's the interaction between the blurry and focused elements of your picture.

For instance, a photograph of a flower with the entire background showing as blurry would have a low depth of field, while a photograph of a long subway platform with both near and far subjects in relatively clear focus would have a high depth of field. In both of these examples, simply changing the depth of field will have a major impact to what the viewer sees in your photograph.

What Influences Depth of Field?

One of the primary influences of depth of field is the length of your exposure. The longer your camera's digital sensor or film has to absorb the image you're shooting, the more detail your camera will produce. Longer exposures will always result in greater depth of field, even if at unperceivable levels.

If you want to change your depth of field, all you have to do is increase or decrease your 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 camera these days will allow you to pick a shutter speed and then will automatically select the right f stop whereas with older cameras you have to adjust the settings yourself.

Helpful Tip: If you want high depth of field pictures then it's likely you'll be working with long exposure times depending upon the quality of light you have. 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.