Guide · Updated
Zone focusing
Set the distance once, then shoot.
Zone focusing is focusing before the picture: you set the lens to a distance, pick an aperture whose depth of field covers the band where your subject will be, and then shoot without focusing again. A 35 mm lens at f/8 set to 3 m (10 ft) is sharp from 1.92 m (6.3 ft) to 6.80 m (22.3 ft) on full frame, so anyone who walks through that stretch is in focus the instant you press the shutter (our arithmetic, with the thin-lens formulas). It is how street photographers use rangefinders and other manual-focus cameras.
The price is choosing in advance: a subject outside the zone is soft, and a deep zone needs a small aperture and enough light for it. On a phone the lens is so short that the zone is nearly everything, which changes the question; that is near the end.
01 · How
How to zone focus
- Pick the zone. Decide how near and how far your subjects will be. Across a sidewalk, that might be 2 to 5 m (7 to 16 ft).
- Pick the aperture. The smaller the opening, the deeper the zone. A 35 mm lens at f/8 set to 3 m is sharp from 1.92 m to 6.80 m on full frame (our arithmetic). In daylight the aperture is usually what you choose first, and the shutter follows.
- Set the distance. On a lens with a depth-of-field scale, turn the focus ring until the zone’s near and far distances sit between the two marks for your aperture. Without one, use a table or the depth-of-field calculator. The focus that splits a 2 to 5 m zone is 2.86 m, not 3.5 m: on the scale it is the halfway point, and the scale is spaced by one over the distance.
- Set the shutter. Fast enough for people walking, from the light: at f/8 on ISO 400 film in bright sun, sunny 16 gives 1/1600 s (two stops more light than its f/16 at 1/400 s).
- Learn the distance. Judge 3 m by eye, check it by pacing it off, and practice until the guess is right. The zone forgives a small error; it does not forgive 3 m taken for 8.
- Shoot without refocusing. Keep your subjects inside the zone by moving yourself, not the ring. The camera is ready the instant you raise it.
The sunny 16 numbers are from the sunny 16 calculator; the zones from the depth of field calculator, which takes any lens, aperture and format.
02 · The scale
How to read a depth-of-field scale
Many manual-focus lenses carry two scales. The distance scale turns with the focus ring; the depth-of-field scale under it is fixed, with the focus index in the middle and a pair of marks for each aperture either side. Whatever distances sit between the pair for your aperture are sharp.
The scale is not spaced evenly in meters. It is spaced by one over the distance, which is how a lens’s helicoid moves, so the marks bunch toward infinity, and the depth-of-field marks can stay fixed because the sharp band has nearly the same width on that scale at every distance. It is also why the focus that splits a zone sits at the halfway point on the scale, nearer than the halfway point in meters. Lens scales measure from the film plane, the formulas from the lens; the difference is a few centimeters.
03 · Zones
Zone focusing settings for 28, 35 and 50 mm
The sharp zone on full frame with the lens set to 3 m (9.8 ft), at three apertures. Our arithmetic with a circle of confusion of 0.029 mm, the frame’s diagonal over 1500. For other distances and formats, the calculator does the same sum.
| Lens | Aperture | Sharp from | Sharp to |
|---|---|---|---|
| 28 mm | f/8 | 1.60 m (5.3 ft) | 24.0 m (78.6 ft) |
| 28 mm | f/11 | 1.36 m (4.5 ft) | ∞ |
| 28 mm | f/16 | 1.09 m (3.6 ft) | ∞ |
| 35 mm | f/8 | 1.92 m (6.3 ft) | 6.80 m (22.3 ft) |
| 35 mm | f/11 | 1.70 m (5.6 ft) | 12.9 m (42.4 ft) |
| 35 mm | f/16 | 1.42 m (4.6 ft) | ∞ |
| 50 mm | f/8 | 2.36 m (7.7 ft) | 4.12 m (13.5 ft) |
| 50 mm | f/11 | 2.18 m (7.2 ft) | 4.80 m (15.7 ft) |
| 50 mm | f/16 | 1.94 m (6.4 ft) | 6.59 m (21.6 ft) |
Sharp here means a blur no bigger than 0.029 mm on the negative, a common convention. A big print or a tight crop is stricter, and wants a smaller aperture for the same zone.
04 · Or
Zone focusing vs hyperfocal focusing and autofocus
| Method | What you set | Best for |
|---|---|---|
| Zone focusing | A distance and an aperture chosen so a band of the scene (say 2 to 5 m) is sharp. | The street, a crowd, anything that moves through a place you can predict. |
| Hyperfocal focusing | The one zone whose far edge is infinity: focus at the hyperfocal distance, sharp from half of it out. | Landscapes, and the street when the near edge is close enough. |
| Autofocus | The camera focuses on the subject for each frame. | A subject you can point at and wait for, wide apertures, close up. |
Hyperfocal focusing is the zone you choose when you do not know how far things will be. When you do, a nearer zone with its far edge short of infinity is sharper where it counts. Autofocus is the better tool when there is time to point at the subject, or when the aperture is wide and the zone thin.
05 · Phones
Zone focusing on a phone
A phone’s lens is a few millimeters long, and the depth of field grows as the focal length shrinks. On the phone Clack is tested on (a CMF Phone 2 Pro, main camera 5.56 mm at f/1.88, fixed), the hyperfocal distance is 2.75 m (9.0 ft) at a circle of confusion of three pixels: focused there, everything from 1.37 m out is sharp. The zones that a 35 mm lens needs f/16 for are open to the phone at its widest aperture.
| Set to | Sharp from | Sharp to |
|---|---|---|
| 0.30 m | 0.27 m | 0.34 m |
| 0.50 m | 0.42 m | 0.61 m |
| 1.00 m | 0.73 m | 1.57 m |
| 1.50 m | 0.97 m | 3.30 m |
| 2.75 m (hyperfocal) | 1.37 m | ∞ |
So on a phone, zone focusing is a close-range technique. For anything past about 1.37 m there is one setting, the hyperfocal distance, and nothing to plan; under a meter the zone is thin, and a set distance still saves the moment autofocus spends finding it. If your phone’s camera app has a manual or pro mode with a focus slider, set it there; many apps also lock focus with a long press on the finder, which holds a distance the same way.
06 · Clack
Zone focusing in Clack
Clack is a film camera app for Android. Focus is automatic: a tap on the finder focuses there and holds (AF-L lights), and a tap on AF-L goes back to autofocus. Holding a tapped distance is the quick way to pre-focus. Where the phone’s camera offers manual focus, a setting, Manual focus, adds a focus ring for setting a distance by hand. It is off by default, for the reason in the section above: on the tested phone’s lens, everything past about 1.37 m is sharp at one setting, so setting a distance by hand matters only close up.
- A lens barrel’s scale
- The ring is a tape marked in meters and spaced by one over the distance, as engraved on a lens, with a bracket across the sharp band and the band written beside it (for example “1.4 m – ∞”). It slides with no detents, and stays where you left it from frame to frame.
- The band
- Computed from the distance you set at a circle of confusion of three pixels, the numbers in the table above. While focus is set, the finder shows it too.
- Back to autofocus
- Push the ring past ∞ and it goes back to autofocus. A tap on the finder focuses there and stays manual.
- Approximate
- The tested phone reports its focus distances as uncalibrated, so the meter marks are approximate; the marks and the band share the same approximation.
AF-L and the focus ring appear only on phones whose camera offers manual focus. On the others focus is automatic, with tap to focus. Tested mostly on the CMF Phone 2 Pro.
AndroidComing soon to Google Play. More about Clack
Questions
- What is zone focusing?
- Setting the focus to a distance before you shoot, with an aperture whose depth of field covers the band where your subject will be, and then shooting without focusing again. It is how street photographers work with manual-focus lenses: the camera is ready the moment something happens.
- Is zone focusing the same as hyperfocal focusing?
- Hyperfocal focusing is one kind of zone focusing: the zone whose far edge is infinity. Zone focusing in general puts the zone wherever the subjects are, which on the street is often nearer, with the far edge short of infinity.
- What aperture should I use for zone focusing?
- Whatever makes the zone deep enough at the shutter speed the light allows. On a 35 mm lens on full frame set to 3 m, f/8 covers 1.92 m to 6.80 m and f/16 covers 1.42 m to infinity (our arithmetic). Longer lenses need smaller apertures for the same zone.
- What does “f/8 and be there” mean?
- A saying about street and news photography: set the camera to something deep and reliable, and put your effort into being where the picture happens. It is often credited to the news photographer Weegee, though Wikipedia calls that credit spurious.
- How do you zone focus without a depth-of-field scale?
- Read the near and far limits from a depth-of-field table or calculator, then set the distance on the lens’s focus scale, or autofocus on something at that distance and switch the lens to manual focus so it stays there.
- What is scale focusing?
- Focusing by setting the distance on the lens’s scale from an estimate, rather than by looking: the way cameras with no rangefinder or focusing screen are focused. Zone focusing is scale focusing with the depth of field planned in.
- Can you zone focus on a phone?
- Where the phone’s camera offers manual focus, yes, but for subjects past about 1.37 m it gains little. The lens is so short that on the tested phone everything from 1.37 m to infinity is sharp when it is focused at 2.75 m (our arithmetic, at a circle of confusion of three pixels). It matters close up: set to 1 m, the sharp band is 0.73 m to 1.57 m.
Sources
- Depth of field (Wikipedia): the depth-of-field scale, and focus from the limits
- Hyperfocal distance (Wikipedia)
- Circle of confusion (Wikipedia): the d/1500 criterion
- Weegee (Wikipedia): on “f/8 and be there”
Every distance on this page is our arithmetic with the thin-lens formulas, not a measurement. The phone’s optics are the CMF Phone 2 Pro’s as Clack reads them.