A camera can only focus its lens at a single point, but there will be an area that stretches in front of and behind this focus point that still appears sharp. This is known as the depth of field. It's not a fixed distance, it changes in size and can be described as either 'shallow' (where only a narrow zone appears sharp) or deep (where more of the picture appears sharp). The lower your f-number, the smaller your depth of field. Likewise, the higher your f-number, the larger your depth of field. For example, using a setting of f/2.8 will produce a very shallow depth of field while f/11 will produce a deeper Depth of Field. The closer your object is to the camera, the shallower your depth of field becomes. Therefore, moving further away from your subject will deepen your depth of field.
Shallow depth of field-F/4
When the aperture is large (ex. f/1.8), the area in front and behind the focus point is very slim or shallow. That means that objects right in front and right behind the plane of focus is already going out of focus. The closer your camera is to the subject, the slimmer the plane of focus. A shallow depth of field will reduce the sharpness in your picture.
Medium depth of field-F/11
This means that the object is still clear and sharp but the background isn’t completely blurred out. This gives the photo more depth but the background is still not distracting.
Deep depth of field-F/16
Depth-of-field is controlled by your aperture. When the aperture is small (ex. f/16), the image has a deep or large depth of field. This means that the focus range covers a large area front-to-back, from several yards in front of the focus plane to nearly infinity behind it.