Depth in Field is basically just the distance between two objects, the closest and the furthest objects in the shot.
In film making manual focusing is an important element when making a film. Manual focusing could be used reveal someone or any object more clearly in detail. This technique is really effective in a film and is mainly used in horrors and thrillers. The technique may be used to show the reader which character is important and should be paid more attention to. An example of it being used may be someone in the distance and then someone quite close. Then the camera will be manually focused and adjusted to the person in the distance behind a character, to show suspense. The camera can be manually focused again to show the character closer to the camera in more detail than the one in the far distance.
As well as films manual focusing can also be used in TV Drama.
Here is our video demonstrating manual focus pulling.