Depth of field is the relative distance in front of a subject that is in focus. It applies to any type of images, including those in photography and video. Since clear focus can only occur at a single distance, this becomes the focal point of any image. The field flows outwards in a circle, where the further from the center you get the less focused an image will be from the point of origin. The diameter of the largest circle that still keeps a subject in focus is considered the circle of confusion. Circles of confusion are determined by acuity, perception and whether or not the image itself is enlarged from its original size.

Factors such as blurriness, subject movement and distances between the camera and subject all effect the depth of field of the picture. Areas within the acceptable depth of field will be clear and crisp. Objects outside of that field will appear blurry and out of focus in many cases.

Image sizes also affect depth of field. Larger pictures, enlarged from their original format, will distort portions of the image within the acceptable depth of field. This will change the landscape of the picture and distort bits and pieces that were not meant to be out of focus. When taking a picture, it is important to note the size your camera is saving as well as whether or not you will need to enlarge the picture down the line. Formats can help change the depth of field later on down the line in photo editing software should you need to enlarge the photograph for any reason.

Since bigger formats require longer lenses, they will have a lower depth of field. Thus, the depth of field is controlled by the lens. Lens have f-numbers which reduce the aperture diameter when taking a picture and increases the depth of field in the process. It does, however, reduce light being transmitted, increasing diffraction and placing some limits on what can and cannot be reduced with the aperture. In the film industry, cinematographers will generally stick with two types of apertures, one for interior shots and one for exterior shots, to give consistency throughout the film. Photographers will do the same during series shoots and other types of photographs to stay within the same type of depth of field consistency for the project at hand.Camera movement can also affect the depth of field. Since the lens axis is perpendicular to the plane, the focus is parallel to the image, too. The depth of field will therefore extend between the planes on the sides of the subject, giving you the sharp focus. However, if the lens for some reason is not perpendicular, the image plane is capable of being rotated to change the depth of field. This is accomplished through camera movements, such as tilting or rotating the lens. Since these are available on most view digital cameras nowadays, anybody can take advantage of them to change the depth of field easily. You can also purchase specialty lenses that will allow you to take advantage of camera movements.

When you rotate the plane of focus, the depth of field is no longer parallel and this wedges the subject into a specific focus. Tilting will change the heights of the depth of field, and the width will change with the distance between the camera and the subject. This can change the maximum and minimum parts of the image trapped within the depth of field you are trying to achieve and focus.

Depending on how you set up your particular shot, the depth of field could be tiny or it could go on for infinity. Landscapes in particular are meant to be shot in clear focus throughout the photo, and this requires you to change the normal depth of field you would shoot a picture with a clear subject. More artistic situations might warrant a tilt or rotation of the depth of field to find a very tiny focus or multiple focuses due to subject placement. Backgrounds can be displaced in portraits to focus on the subject only depending on the tightness of the depth of field.

It is important to note that while the depth of field will refocus areas of a picture, it will not make them so unclear as to ruin the photo. Depth of field also cannot determine just how badly areas outside the point of focus will be unfocused, depending on other aspects of the overall picture, the focus could be just off a bit or even more than usual. Tinkering with different settings and the depth of field will show you how your camera reacts to different points of focus and backgrounds to give you the best picture.

While most think depth of field is a complicated subject, any photographer can learn how to apply its principles to their photos and take better pictures. Reading your digital camera's manual, reading up on depth of field and point of focus, as well as practicing out in the field are the simplest ways to learn how to use it to your advantages. Your pictures will come out clear, crisp and your focus will be what you make of it. Only by getting out their and taking pictures will you learn how depth of field can make you a better photographer.