A beautiful way to bring attention to your subject in portrait shots is to blur the background by adjusting the depth of your focus area.
Depth of Field
The area of focused objects in your photos is called depth of field. When taking photos of nearby objects you can adjust your aperture to keep a sharp focus right on your subject while keeping the background out-of-focus. It’s important to note that objects must be nearby for a more shallow depth of field. Using a large aperture and focusing on a distant object won’t create a background blur effect. A larger aperture opening creates a shallow depth of field; a smaller aperture opening provides a near-infinite focus. Lower f-stop numbers represent larger aperture openings. Be careful not to open your aperture too large though, as a sliver of field in focus may blur even detail in your subject.
The Art of Bokeh
While depth of field describes the area in sharp focus in a photo, bokeh is the quality of the unfocused blur at shallow depth of field. Colorful discs of light can make beautiful backgrounds for portrait shots, as seen below:
The portrait above combines sharp focus on the subject and a beautiful bokeh effect in the background. The aperture of the photo is f/2.8 (1/80 shutter, ISO 1600), and the subject is standing very close to the photographer.