Using Differential Focus in Movies
Differential focus is used quite a bit in photography, but it is also utilized in movies. This refers to keeping a small area in focus and then having the background be out of focus or blurred. This tends to emphasize the main subject of the shot. Movies do not use this exclusively, but directors will choose this effect when shooting for special purposes.
In particular, this differential focus is used to instigate audience reactions. This in particular is used when a narrative occurs and the main character is reacting. By holding the focus on the character, it is possible to have the viewer feel what she is feeling, and share that reaction while still getting all the necessary exposition. If a specific emotion needs to be stressed, then differential focus works well.
Revealing Character Conditions
Many times, this differential focus can be used for specific conditions, such as actors that are stoned or someone that has been knocked out and is all fuzzy in the head. This can be an easy way to show someone's consciousness or how focused and individual is without having to put it into words. Instead this lack of focus is showed through the visual of having everything out of focus. Differential focus is perfect for wooziness or if someone is drunk.
Many times, differential focus can be used in war movies for those shots that can be labeled as eye down the barrel. This is a more difficult shot, but is really fabulous when it is done well. Many times, having a lot of shooting can be busy, but when that one important shot comes, the suspense is created by shifting the focus to the gun that is shooting that important bullet.
Differential focus is traditionally used in horror films and melodramas by creating a portrait of a face. The suspense is built by having the person's face is in focus, but the person creeping up on him is out of focus. Many times, what occurs in the background needs to be kept hidden.
Showing or Hiding Details
As with photos, differential focus in movies is used to show or to hide specific details. However, if it is used too frequently, then this can seriously affect the flow of the film. These shots will be planned out in advance, as they are a camera effect and not an after effect. In order to do it well, an experienced camera operator and director of photography is needed.
How It Works
Differential focus is achieved by setting the f number, format and distance to the image that will be focused. It is possible to achieve this effect with all different lenses and cameras as long as the shooter understands the features that affect the depth of field. Depth of file, which is used to create differential focus, can be achieved many different ways. In movies many times, the tile and angle of the camera will be used to create the differential focus. There are several lenses that have been released to help make it easier to change the depth of field. However, this is not a lens effect.