Zone Focus Explained
Written by: Tiffany Joyce
Zone focus is a technique that allows the photographer to essentially “set and forget” the aperture and focus. When used correctly it adds speed and convenience to your shooting experience, especially in situations when fast-moving subjects outpace auto-focus capabilities. Zone focus is also known as “f/8 and be there,” a term that was coined by photojournalists using 35mm film cameras, to describe their rule of thumb for successfully capturing spontaneous images. It also became their mantra, encouraging photographers to just be in the moment, in their surroundings, taking photos as an organic part of the scene.
Prime lenses with aperture rings and distance scales
Using the depth of field (or “distance”) scale and aperture ring found on many prime lenses, you can identify a “zone” of acceptable sharpness while shooting at a specific aperture, from a specific distance away from the subject. To determine the scale, align the desired f-stop number on the aperture ring of the lens with the center indicator on the focus ring (something like a line, dot or triangle). Then look at the range on the focus ring that corresponds with the f-stop you selected, and that will line up with a distance range on the distance scale. Take a look at this example (mostly, but not quite, to scale):
The red box indicates that f/8 is lined up with the dot on the focus ring. The blue lines indicate the zone of focus this provides – in this case from as close as just under four feet, to as far as about 30 feet (or 1.2 meters to about 9 meters). The infinity mark, which I forgot to add to the illustration, would be on the far right hand side of the distance scale. So if that appears “between the lines” it means that the far end of the zone of focus is to infinity.
Here’s a tip: if the shutter speed is too fast or too slow to correctly expose the subject, simply increase or decrease the ISO, or choose another aperture and use the related distance scale accordingly. And remember to turn off auto-focus!
No scale, or zoom lens?
Now, what do you do if your lens doesn’t have an aperture ring and/or a distance scale (or if the scale is kind of useless, as in the case of my Canon 50mm f/1.4 that only indicates the range for f/22)? Or, what if you’re using a zoom lens? Does that mean you can’t use zone focus? Not at all! You just have to have a depth of field calculator handy, like this one. You can also print out a chart for your specific lens/camera/focal length combo, which is easy to tuck into your camera bag or in your pocket. And yes, there’s also an app for that!
Using the depth of field calculator, I can determine that when using a 100mm lens on my Canon 7D, at f/8, with a subject that is 25 feet away, the near limit is 22.4 feet and the far limit is 28.2 feet. This means that everything within the 5.79 feet between those two limits will be in focus. This is good to keep in mind when you have a moving subject. For that specific reason, understanding the relationship between focal length and aperture, and how they impact the area of focus, is key.
- The smaller the focal length, the greater the area in focus at the same aperture when the distance to the subject is constant. Consider these two calculations for my Canon 7D. Using a 100mm lens at f/8 with a subject that is 25 feet away, the near limit is 22.4 feet and the far limit is 28.2 feet, leaving an area of 5.79 feet in focus between those two points. If I use the same calculations but substitute the lens with a 50mm, the near limit is 17.2 feet and the far limit is 46.3 feet, meaning there is 29.2 feet of “wiggle room”. Conversely, the greater the focal length, the smaller the area of focus at a consistent aperture and distance to subject.
- The smaller the aperture, the greater the area in focus at the same focal length when the distance to the subject is constant. So, when using a 100mm lens at f/8 with a subject that is 25 feet away, the near limit is 22.4 feet and the far limit is 28.2 feet, leaving an area of 5.79 feet in focus. If I use the same calculations but substitute the aperture for f/11, the near limit is 21.5 feet and the far limit is 29.8 feet, leaving 8.3 feet of “wiggle room”. Conversely, the greater the aperture, the smaller the area of focus at a consistent focal length and distance to subject.
- The closer the subject, the shorter the zone in focus will be when aperture and focal length are constant. For instance, when using a 50mm lens at f/8 with a subject that is 20 feet away, the depth of field is between 14.6 and 31.6 feet, with everything inside the 17 feet in between in focus. However, if the subject is only 5 feet away, the depth of field drops to everything between 4.59 feet and 5.49 feet, leaving only a focus zone of 0.9 feet.
If you’re using a zoom lens, you just have to look up the calculation for the focal length you are using at the time. It’s hard, I know, to keep in mind that you can’t touch that zoom ring! So if you’re using, say, a 70-300mm lens, I would recommend printing out the depth of field chart for 70mm, 135mm, and 300mm to cover your bases.
Since distance from the subject is a key factor in these calculations, what if you’re just not good at figuring out distances (or completely inept, like my husband claims I am)?
- If you’re shooting a landscape photo using a small aperture to get everything in focus, you probably don’t need to worry very much since the far limit will usually be “infinity”. Just estimate the distance to the first point of foreground interest – 15 feet, 20 feet, etc.
- A football field is 300 feet long and has handy hash-marks at 10-yard increments. A basketball court is 94 feet long, and half-court is at 47 feet. If you know this, it’s easy to figure out, based on where you happen to be standing or sitting, the distance to the subject.
- Measure your stride. My stride just happens to be almost exactly three feet, so I can easily pace off the distance and do the math in my head.
- Your arm length is about half your height. If you measure your arm span from fingertip to fingertip, you will find that it (usually) almost exactly matches your height. So if someone or something is an arm’s length in front of me personally, and I’m 5’3″ tall, it’s 31.5 inches (or two feet 7.5 inches) away from me.
Has this been clear, or have I utterly confused you all? Have you used this technique before? We’d love to hear about your experience, and see your photos! Please share with us in our Flickr Group or on our Facebook Page.
Photo credits (in order of appearance):
- “Canon FD 200mm f/2.8 S.S.C. Lens” by S58Y on Flickr Creative Commons.
- “Four Peaks” and “Lettuce Wrap” by Tiffany Joyce
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