Focus and depth of field

Focus is a plane, depth of field is a zone

When you focus, the lens makes one distance perfectly sharp. Strictly speaking, only that plane is in focus.

Things a little nearer or farther are slightly blurred, but if the blur is too small for your eye to notice at normal viewing size, they still look sharp. That acceptably sharp zone is the depth of field.

So the question is never just “is it in focus?” but also “how much in front and behind is sharp?”

What makes depth of field deeper or shallower

Aperture: the biggest lever. f/1.8 gives a thin slice; f/11 gives a deep zone.

Distance: the closer you are, the shallower it gets. A flower 1 ft away may have less than half an inch of sharpness at f/4, while a building 100 ft away is sharp at almost any setting.

Focal length: at the same distance, a 200 mm lens gives much shallower depth of field than a 24 mm lens.

Sensor size: for the same framing and f-number, a larger sensor gives shallower depth of field. This is why phones keep almost everything sharp and need software to fake background blur.

The image on this page shows the same scene at several apertures side by side: watch the background go from soft to sharp as the f-number grows.

The one-third rule and hyperfocal distance

At ordinary distances, about one third of the sharp zone lies in front of the focus point and two thirds behind it. This is only a rule of thumb: up close it is nearer half and half, and at long distances the zone behind stretches much further. Focusing about a third of the way into a scene is a good starting point.

Hyperfocal distance is the focus distance that makes everything from about half that distance to the far horizon look sharp. For example, with a 24 mm lens on a full-frame camera at f/8, it is roughly 8 ft: focus there and things from about 4 ft to infinity look sharp (approximate, depends on how strict your sharpness standard is).

Use the calculator below to get the near limit, far limit and hyperfocal distance for your own lens and settings.

Bokeh: the quality of the blur

Bokeh is not how much the background is blurred but how that blur looks. Some lenses turn out-of-focus lights into smooth round discs; others make busy, ring-edged or cat-eye shapes.

To get more of it: use a wide aperture, get close to your subject and put plenty of distance between the subject and the background. A background 30 ft behind a portrait blurs far more than one 3 ft behind.

Autofocus modes and focus points

Single autofocus (often AF-S or One Shot) locks focus when you half-press the button and keeps it there. Best for still subjects such as landscapes, products and posed portraits.

Continuous autofocus (AF-C or AI Servo) keeps adjusting as long as you hold the button, following a subject that moves toward or away from you. Best for sport, pets, children and birds.

Focus points decide where the camera focuses. Letting the camera choose often picks the nearest or brightest object; choosing a single point yourself, or using eye detection where available, puts focus exactly where you want it. In portraits, the nearest eye should be sharp.

Practical settings by genre

Portraits: f/1.8 to f/2.8, single AF or eye detection, focus on the nearest eye. With a very wide aperture up close, both eyes may not be sharp; f/2.8 to f/4 helps.

Groups: f/5.6 to f/8 so that people in different rows stay sharp; focus on someone in the front third of the group.

Landscapes: f/8 to f/11, focus about a third into the scene or at the hyperfocal distance.

Street: f/8 with a wide lens, focus preset to about 10 ft, so most things in front of you are sharp without waiting for autofocus.

Macro: depth of field is tiny even at f/11; focus by moving slightly forward and back rather than turning the focus ring.

Sport and wildlife: f/2.8 to f/5.6, continuous AF and a group of focus points to follow the subject.