How to calculate depth of field

How much of the scene is acceptably sharp, and where to focus so that the most of it is.

Only one distance is ever truly in focus. Depth of field is the zone either side of it that looks sharp enough, and "sharp enough" depends on how large the picture will be viewed — which is why the number is a convention rather than a physical constant.

Step-by-step

1. Choose your sensor size. This sets the circle of confusion the calculation uses.
2. Enter focal length, aperture and focus distance.
3. Read the near and far limits, the total depth, and the hyperfocal distance.

The four things that change it

• Aperture. Stopping down deepens it. The most direct control.
• Focal length. Longer lenses give less depth at the same distance and framing.
• Focus distance. The dominant factor — depth grows roughly with the square of the distance, so close focus is where depth vanishes.
• Sensor size. Smaller sensors give more depth at the same equivalent framing.

The one-third rule is only sometimes true

Depth is often said to extend one third in front of the focus point and two thirds behind. That holds at moderate distances and breaks down at both ends: in macro work the distribution is nearly even, and near the hyperfocal distance the far limit runs to infinity. Use the numbers rather than the rule.

Hyperfocal distance

Focus at the hyperfocal distance and everything from half that distance to infinity is acceptably sharp. It is the maximum depth available at a given aperture, which makes it the standard landscape technique.

The catch is that infinity is only just acceptable — stars and distant horizons look soft. If the far distance is the subject, focus there instead and accept less foreground.

Frequently asked questions

Why do the numbers differ between calculators?

Because they assume different circles of confusion — the standard for how much blur counts as sharp. Different sources use different values, and none is more correct than another.

Does sensor size really change depth of field?

At the same framing and aperture, yes. A smaller sensor needs a shorter lens for the same field of view, and shorter lenses give more depth.

Where should I focus for a landscape?

At the hyperfocal distance for maximum overall depth. If the distant horizon is the subject, focus on it instead — hyperfocal makes infinity only marginally sharp.