Depth of field: how to control what is sharp and what is blurred

Depth of field is the zone of a photo that looks acceptably sharp. A shallow depth of field isolates the subject; a deep one keeps the whole scene clear. You control it with three things.

1. Aperture

Wider apertures (smaller f-numbers) make the zone thinner. f/1.4 can give a few centimeters of focus at close range; f/11 can cover a whole room.

2. Distance to the subject

The closer you are, the thinner the depth of field. That is why macro photos need f/8 or more, and why a headshot at f/2.8 has a softer background than a full-body photo at the same aperture.

3. Focal length and background distance

Longer lenses magnify the background, making blur look stronger. Moving the subject away from the background, a few meters from a wall, increases blur dramatically even at moderate apertures.

For a blurred background

Use a fast prime like an 85mm f/1.4 or 50mm f/1.2, get close, and leave plenty of distance between subject and background.

For everything sharp

Use f/8 to f/11 with a wide lens, focus about a third of the way into the scene, and use a tripod if the shutter speed gets slow. For extreme cases, focus stacking combines several photos focused at different distances.