4 Key Factors of Aperture

F-Stop
The aperture is responsible for controlling exactly how much light is allowed to enter the camera lens. Aperture has a direct affect on the depth of view of a image. Altering the F-Stop will impact on the depth of field of the final image/film. A lower F-Stop will allow more light to enter the camera lens, which results in a more shallow depth of field; whereas, a higher F-Stop will allow less light to enter the camera lens, which results in a wider depth of field.

Focal Length
The focal length refers to the size of the camera lens. A longer the focal length (Telephoto) results in less scenery being captured. This camera lens is especially useful in instances when the photographer wants to capture an image that draws the audience's attention to a certain aspect; for example, if a director is trying to point the audience's focus to two characters engaging in a conversation, a telephoto lens would be the first choice pick.
Alternatively film makers may also choose to use a wide angle lens when trying to acquire panorama-styled footage. This enables more of the scenery to be presented to the audience. This is especially useful in scenes shot with establishing shots, where more landscape footage is preferred.

Focal Distance
In its simplest definition, the focal distance is the space between a photographer/film maker's camera and his subject (The person/object he is acquiring footage of).

Physical Depth
Physical depth is the space between to subjects that be captured as the depth of field in an image/recording. In order to see the effects of Depth of Field, there will need to be some physical depth behind the subject.