1. Focus and Depth of Field?
The area in front of the
camera that appears sharp in
the frame is called depth of
field. Depth of Field is
defined as the range of
acceptable focus on a shot.
Depth of field is an
important concept for cinematographers and camera
operators to master because they often need to manipulate
focus to achieve a desired effect.
Selective focus, for instance, draws the
audience’s attention to a specific
portion of the frame. Depth of field can
be either shallow or deep. Shallow
depth of field is the kind in which part of the frame is soft or
out of focus. Thus, the areas of focus or sharpness are
limited. Deep depth of field, on the other hand, is the kind in
which the entire frame, from the foreground to the
background, is sharp or in focus.

2. These three parts of the camera affect depth of field:
1.Aperture
2.Focal length
3.Focus distance
The aperture is the factor that most influences depth of field. The wider the
aperture is, the shallower depth of field will be. A low f-number such as f/2.8
will likely render an image with some soft focus. Conversely, the narrower the
aperture is, the deeper depth of field will be.

3. The figure below illustrates the relation between aperture and the amount of
depth of field. For this illustration, image that the camera is on the left hand
side of the image, represented below by the aperture. The 100mm value
represents the focal length of the lens, which does not change in this scenario: