Zone Focus Explained | Beyond Mega Pixels

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ZONE FOCUS EXPLAINED

Friday, 23rd March 2012

Written by: Tiffany Joyce

Zone focus is a technique that allows the photographer to essentially set and forgetthe 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, encour-

aging 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
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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 linesindicate 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 dis-

tance scale. So if that appears between the lines it means that the far end of the zone

of focus is to infinity.

Heres 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 relateddistance scale accordingly. And remember to turn off auto-focus!

No scale, or zoom lens?

Now, what do you do if your lens doesnt 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 youre using a zoom lens? Does that

mean you cant use zone focus? Not at all! You just have to have a depth of field calcu-lator handy, like this one. You can also print out a chart for your specific lens/cam-

era/focal length combo, which is easy to tuck into your camera bag or in your pocket.

And yes, theres 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.
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(f/11.0 at 31mm, subject at 20 feet = near limit 8.49 feet, far limit infinity)

- 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 theaperture 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 fo-

cus at a consistent focal length and distance to subject.
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(f/1.4 at 50mm, subject at 3 feet = near limit 2.97 feet, far limit 3.03 feet)

- 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 youre using a zoom lens, you just have to look up the calculation for the focal

length you are using at the time. Its hard, I know, to keep in mind that you cant

touch that zoom ring! So if youre 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.

Determining Distance

Since distance from the subject is a key factor in these calculations, what if youre just

not good at figuring out distances (or completely inept, like my husband claims I

am)?

- If youre shooting a landscape photo using a small aperture to get everything in fo-

cus, you probably dont need to worry very much since the far limit will usually be in-

finity. Just estimate the distance to the first point of foreground interest 15 feet, 20

feet, etc.
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- 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, its 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 fin-

gertip to fingertip, you will find that it (usually) almost exactly matches your height.

So if someone or something is an arms length in front of me personally, and Im 53

tall, its 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? Wed love to hear about your experience, and see your photos! Please sharewith 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 byS58Yon Flickr Creative Commons.

- Four Peaks and Lettuce Wrap by Tiffany Joyce

Related posts:

1. Depth-of-Field In Depth

2. Auto Focus Microadjustments

3. Hyperfocal Distance: Maximizing Your Depth of Field

4. Photography 101: Fixed Aperture Explained

5. The Finer Points of Focus

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Zone Focus Explained | Beyond Mega Pixels

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