Aperture affects depth of field: the zone in front of and behind your focus point that looks acceptably sharp.

Key point: there is no single f-number that works for every situation. Depth of field depends on aperture, subject distance, and focal length.

• Wide apertures like f/1.8 give very shallow depth of field, so they are usually poor for large groups or subjects spread across different distances.
• Smaller apertures (higher f-numbers) increase depth of field, which helps keep multiple rows of people, more of a face/body, or subjects at different distances in focus.
• The farther away you are from the subject, the greater the depth of field for the same lens and aperture.
• A shorter focal length also gives more depth of field than a longer one at the same framing conditions.

For two people at different distances, focus carefully and stop the lens down enough so both fall within the depth of field. For groups on a field, you usually need a relatively small aperture and enough distance from the group.

Because the exact result varies, the most practical advice is to use a depth of field calculator for your lens, distance, and camera.