Depth of field

How much of the photo is sharp, from a thin slice to front-to-back.

What controls it

Three things: aperture, how close you are to your subject, and focal length. A wide aperture (low f-number) and getting close both shrink the zone of sharpness; a narrow aperture (high f-number) widens it.

When to use which

Shallow depth around f/1.8 isolates a subject against a soft background. Deep depth, f/8 to f/16, keeps a landscape sharp from foreground to horizon.

See it

Example photo coming soon

One subject shot at f/1.8, f/8, and f/16, so you can see the background go from soft to sharp.

Try it

Frame one subject with something in the background, then shoot it wide open and stopped down. Compare how much falls away.