Zone focusing (sometimes called scale focusing) allows a photographer to know what will be in focus without even looking through the viewfinder. It’s an invaluable technique that’s often used in street and other types of photography where speed and spontaneity are factors. It can help us get the shot when autofocus lag or direct manual focusing would otherwise cause us to miss it.
It can sound complicated, but it’s not, as long as you understand depth-of-field (DOF) and how a photographer influences DOF. For those unfamiliar with the concept of depth-of-field, the basics are simple – as a lens aperture is stopped down, the zone of focus of the image increases in depth. Larger apertures (lower F numbers) yield very shallow depth of field, creating images that isolate the subject in focus while blurring the background and foreground into pleasant bokeh. Smaller apertures (higher F numbers) create images in which more of the composition is in focus, perfect for landscapes and photojournalism.
Zone focusing uses this understanding of depth-of-field to allow the shooter to know what parts of the photograph will be in focus by simply looking at the camera lens. Most manual focus lenses and some AF lenses have a distance scale on their focusing ring and barrel to indicate which areas of a composition will be in focus based on the set aperture. By looking at the focus ring in relation to the focus scale, it’s possible to see that when set to F/8, for example, everything that falls between the markers for “8” on the focus scale will be in focus. As you spin the focus ring, the distance scale rotates to show that the area in focus is changing.
Let’s illustrate the point. In the left photo of the lens below, we can see the lens aperture has been set to F/8. Looking at the depth-of-field scale and focusing ring we can see that when set to F/8, the final image will have a zone of focus that spans from infinity to 10 feet away. If we then change the aperture to F/16 we can see that the final image will have a zone of focus that spans from infinity to 4.5 feet away. Within these spans, the image will be acceptably sharp.
Using this technique, the shooter sets the aperture and then simply makes sure the subject is within the marked distances when taking the shot. This allows for rapid and candid shooting, crucial in street photography, or when fast moving subjects negate the possibility of viewfinder composition.
But remember that depth-of-field is a gradual change. The exact point of focus is still whatever distance is directly in the middle of the zone of focus (usually marked on the lens by a straight line projecting from the set value on the aperture ring), and depth-of-field gradually decreases in front of and behind that point of focus. But an area of this zone should be rendered acceptably sharp in the final image. This relates to the classically confusing photographic concept called the Circle of Confusion.
Because of this, it’s still important to be able to accurately estimate your distance to subject and release the shutter at the right moment. Even if your zone focus indicates it will cover subjects from 20 feet to 2 feet away, you’re still best served to shoot when the subject is approximately 10 feet from the camera.
It’s also important to note that lenses of different focal lengths produce intrinsically different depths-of-field. A wide-angle lens, for example, produces greater depth-of-field at numerically identical apertures. See below, where the 50mm set to F/8 produces a focus zone from infinity down to fifteen feet whereas the 18mm lens set to F/8 produces a focus zone from infinity way down to three feet. Because of this, zone focusing is a technique best used with wide or wide-standard lenses (though with practice it can be used effectively with longer focal length lenses).
[The photos below were made with the Rollei 35, a zone focusing camera.]
See? Zone focus is a pretty simple concept once we’ve visualized it. In fact, back in the earlier days of photography there were plenty of cameras that only used zone focus. Just take a look at Zeiss’ beautiful Contina or the amazing Rollei 35. These great cameras certainly aren’t hampered by their being exclusively zone focus machines.
Today, zone focusing is most useful to photographers who are using viewfinder or rangefinder cameras with manual focus lenses, but shooters using SLRs and modern machines can also benefit from this knowledge.
It’s an especially useful technique for when we’re trying to be inconspicuous. That’s why so many street photographers use it. With zone focusing, we don’t even need to hold the camera up to our eye to get the shot. We can shoot from the waist or make snapshots in the run-and-gun style popular with so many modern street shooters. It’s even useful when we do have time to peer through a viewfinder – by zone focusing we can concentrate entirely on composition and framing and forget about focusing. One less thing to worry about.