--The lower the f/stop—the larger the opening in the lens—the less depth of field—the blurrier the background.

  --The higher the f/stop—the smaller the opening in the lens—the greater the depth of field—the sharper the background.

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We use focus and depth of field to direct attention to what is important in the photograph, and we use lack of focus to minimize distractions that cannot be eliminated from the composition. While there are no rules, there are some guidelines.

  --For classic portraiture we separate our subject from the surroundings by using "selective focus." Choosing a large aperture (lower f/stop, like f2.8) creates very shallow depth of field with only the subject, or just a portion of the subject, in focus. This helps direct the viewer's attention to the subject.

  --In a landscape or scenic photograph we usually want to see as much detail as possible from foreground to background; we want to achieve the maximum depth of field by choosing a small aperture (higher f/stop, like f/8 or f/11).

-Videographers and cinematographers use Depth-of-Field to your advantage to create more interesting shots for your videos. The same way that photographers use a shallow depth of field to separate a subject from its background, or deep depth of field to ensure everything in a scene is in focus from the foreground to the background—you can use these techniques in your videos.