Technically, “depth of field” (DOF) is the optical phenomenon of a lens that expresses the distance about the plane of focus where objects appear acceptably sharp in an image. Creatively speaking, it’s the relative degree of sharpness between objects that are close to or farther away from a lens. When both distances, near and far, are sharp the DOF is said to be “long” or “deep.” When only the point of critical focus is sharp with the background out of focus, the DOF is “narrow” or “shallow.”
There are mathematical considerations that affect the DOF, but in practice, the features that concern the photographer are a) the lens’s aperture or f-stop, b) the focal length of the lens, and c) the camera-to-subject distance. Each is an independent variable, but they combine to produce the DOF.
At one extreme, long depth of field—where objects near and far are sharp—spreads the viewer’s attention over the entire image, encouraging the eye to explore all of the details within the frame. When a lens is “stopped down,” admitting little light, the f-stop numbers hover around f16, f22, f32. The higher the number, the longer the DOF. In this range, when “critically focusing” on a near subject, the background will also be sharp—sharper at f32 than at f16.
At the other extreme, narrow DOF compels the eye to stay focused on the point or in the area where the subject is sharpest. DOF is controlled by the choices of aperture, lens and distance from the subject. When the lens is “wide open,” admitting more light, the f-stop numbers hover around f1.4, f2.8, f 3.5, f4. The lower the number, the narrower the DOF. In this range, when critically focusing on a near-to-the-camera object, the background will be out of focus.
Focal Length of the Lens
The focal length of a lens determines the magnification at which it images distant objects. From a given position, a “wide angle” lens will show the sky, plaza, and fountain. (Fountain Square, downtown Cincinnati)
A “medium” or “normal” focal length lens will show a bit of sky, buildings, and details on the fountain.
And a telephoto lens will exclude everything except the fountain and what’s behind it. Here, the camera’s aperture was fairly wide open, rendering the building out of focus.
A very wide angle lens, even with the aperture wide open, will likely render both the foreground and background as sharp. Conversely, the aperture of a telephoto lens has to be “stopped down” considerably in order to keep the background sharp. This is one of the reasons why professionals carry many lenses—or a zoom lens where the focal length can be varied from wide to telephoto. (“The Genius of Water” atop the Tyler Davidson Fountain in Cincinnati).
As a camera comes closer to the primary subject, the foreground and background in the frame tend to go out of focus, necessitating a smaller aperture to make them sharp. As the distance is increased, objects, both near and far, tend to be in focus. The camera moving closer to a subject is equivalent to a person moving closer. It’s why in movies, directors prefer to use single focal length (“prime”) lenses rather than a zoom lens. They want the viewer to feel like they are in his or her personal space.
Reflections On “Personal” Depth Of Field
Our eyes shift from wide to medium to closeup perspectives seemingly in an instant. In photography, we refer to these “fields” as if a setting, for instance, a landscape, consists of separate planes or areas. Of course, they don’t. They’re continuous in our experience. Where the camera is a single and objective “eye” that only records in two dimensions, we not only have two eyes that allow us to see in three dimensions, our perception is subjective—we make sense of what’s in front of us—or imagined.
This observation is so obvious, it hides the significance of perception as a process of thoughts that make meaning, which in turn drive action. If we consider a field then, as a domain of thought, of consciousness, the question arises: What is my personal depth of field? Considering my thoughts, how deep do they go? Most of the time, when I’m not focused on everyday concerns, where do I place my focus? Certainly, like a zoom lens, we shift between close-in, self-oriented and short-term matters, and broader, more other-directed and long-term thinking. As with a camera, it’s under our control.
As an organism starts to develop it begins to resonate to a certain field, and the more the organism follows that particular path the more it becomes habituated and goes on developing within that field to its final form.
Becoming habituated to a particular field is like viewing the world solely through a “normal” lens. But in every day living our personal DOF shifts continuously. Looked at analogously, it provides a framework for self-reflection. For instance, a camera’s aperture controls the amount of light that reaches the recording medium. So how much light—the light of awareness—am I letting in by exposing myself to diverse perspectives, higher consciousness, creative and inspirational sources? What is currently the depth of my thought-field?
Consider also the focal length of a lens that determines the extent of coverage. Am I taking advantage of opportunities to change lenses, to empathize, walk in other people’s shoes, to expand my field of thinking by observing people and circumstances close up, broadly, and farther away in order to supplement my “normal,” routinized ways of thinking?
And with regard to camera-to-subject distance, am I venturing out, exploring other fields of thought, ideas, and values? Of course, there are no right or wrong, better or worse, responses to these questions, but I believe they provide some interesting touchstones when considering where we are in the unfolding process of trying to live our lives more authentically.
A person has not only perceptions but a will to perceive, not only a capacity to observe the world but a capacity to alter his or her observation of it — which, in the end, is the capacity to alter the world itself. Those people who recognize that imagination is reality’s master we call “sages,” and those who act upon it, we call “artists.”
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