Depth of field (DoF) is the zone of a photo, in front of and behind the point you focused on, that looks acceptably sharp. Everything closer than the near limit or farther than the far limit is progressively blurred. Controlling it is one of the most expressive decisions in photography: a thin sharp zone isolates a subject from its surroundings, a deep one tells the story of a whole place.
"Acceptably sharp" and the circle of confusion
Strictly speaking a lens focuses perfectly at only one distance. A point slightly in front of or behind it is recorded as a tiny disc of blur. As long as that disc is smaller than the eye can resolve in the final image, it still looks like a point. That largest acceptable disc is the circle of confusion (CoC). The usual convention — used by lens distance scales, DOFMaster and our depth of field calculator — is the sensor diagonal divided by about 1,440: 0.030 mm for full frame, 0.020 mm for APS-C and 0.015 mm for Micro Four Thirds.
The convention assumes an 8 × 10 inch print viewed from about 25 cm by someone with normal eyesight. That has an important consequence: depth of field depends on how the photo is viewed. A sharp zone that looks fine on a phone may look soft on a large print or when you zoom to 100% on a 45 MP file. If you work that way, halve the circle of confusion under Advanced in the calculator.
The four things that control depth of field
1. Aperture
The f-number is the easiest control. A wide aperture (small number such as f/1.8) gives a thin sharp zone; a narrow aperture (f/8, f/11) gives a deep one. Each full stop multiplies the depth of field by about 1.4. With a 50 mm lens on full frame focused at 3 m, f/1.8 gives 38 cm of sharpness, while f/8 gives 1.85 m:
2. Focus distance
Distance has the strongest effect of all, because depth of field grows roughly with the square of the focus distance. Halve the distance and the sharp zone shrinks to about a quarter. The same 50 mm f/1.8 that gives 38 cm at 3 m gives only 9.4 cm at 1.5 m. This is why close-ups and macro shots have such thin focus even at f/8, and why distant landscapes are easy to get sharp.
3. Focal length
At the same distance, a longer lens gives less depth of field — again roughly with the square: double the focal length and the sharp zone shrinks to a quarter. But photographers rarely change focal length while standing still; they step back to keep the same framing. When you do that, something surprising happens: depth of field stays almost the same. Here is a head-and-shoulders framing at f/2.8 on full frame with four different lenses:
| Lens | Distance for same framing | Depth of field |
|---|---|---|
| 35 mm | 2.1 m | 61 cm |
| 50 mm | 3 m | 60 cm |
| 85 mm | 5.1 m | 60 cm |
| 135 mm | 8.1 m | 60 cm |
The sharp zone is nearly identical. What changes is the background: a longer lens shows a smaller slice of it, magnified, so it looks more blurred and closer. That "compression" is why portrait photographers love 85–135 mm lenses even though the depth of field is no thinner than with a 50 mm.
4. Sensor size
A smaller sensor needs a shorter lens to frame the same picture, and a shorter lens means more depth of field. A 25 mm f/1.8 on Micro Four Thirds frames like a 50 mm on full frame, but focused at 3 m it gives 78 cm of depth of field — close to the 78 cm of a 50 mm at f/3.6 on full frame, not the 38 cm at f/1.8. The rule of thumb: multiply the f-number by the crop factor to compare depth of field across formats. The crop factor guide covers this in detail.
In front of and behind the subject
The sharp zone is not centred on the focus point. At moderate distances roughly a third lies in front and two thirds behind; with the 50 mm f/8 example above, 66 cm is in front of the subject and 1.19 m behind. As you focus closer, the split approaches half and half. As you focus farther, the far limit races away faster than the near limit, until at the hyperfocal distance it reaches infinity. The diagram in the calculator shows this split for any setting.
A practical consequence: if you need two things sharp at different distances — say, two rows of people — focus about a third of the way into the gap rather than halfway.
Depth of field is a gradient, not a wall
The near and far limits are where blur crosses a chosen threshold. Objects just outside them are only slightly soft; objects far outside are very blurred. How quickly the background melts away depends on the absolute size of the blur disc, which is why an 85 mm f/1.8 portrait with 5.7 cm of depth of field at 2 m has a much creamier background than a wide-angle shot with similar depth of field: the telephoto magnifies the blurred background.
Settings by genre
- Portraits: f/1.4–f/2.8 with 50–135 mm. Focus on the nearest eye. For groups, f/4–f/5.6 and keep everyone on the same plane.
- Street: f/5.6–f/8 with 28–35 mm and zone focusing at 2.5–3 m, so you never wait for autofocus.
- Landscape: f/8–f/11 with a wide lens focused near the hyperfocal distance; focus stack when the foreground is very close.
- Macro: f/8–f/16 still gives only millimetres; use focus stacking for whole insects or flowers.
- Products and food: f/5.6–f/11, angle the camera so the important plane is parallel to the sensor.
Common misconceptions
"Smaller apertures are always sharper." Beyond about f/11 on full frame, diffraction softens the whole image, so f/22 trades sharp edges for a soft everything. "Telephotos have less depth of field." Only at the same distance; at the same framing the difference is small. "Crop sensors don’t blur backgrounds." They do — you just need a faster lens to match full frame, for example f/1.4 on APS-C to look like f/2 on full frame.
Try these ideas with your own gear in the calculator or look up a specific lens in the depth of field tables. To see the maths behind the numbers, with three worked examples, read the depth of field formula explained.