A Split Focus Diopter is half convex glass that attaches in front of the camera’s main lens to make half the lens nearsighted. The lens can focus on a plane in the background and the diopter on a foreground element. In the 1970′s and 1980′s, Brian De Palma championed the use of this tool to enhance the visual and emotional experience of his films.
The Split Diopter allows for Deep Focus cinematography but requires much less light. It also delivers a distinctive look that blends sharp and out-of-focus imagery all in one frame. Subjects in both foreground and background can be kept in focus. In the video below are all 15 Split Diopter shots from Brian De Palma’s film Blow Out (1981).
You have probably seen many Split Diopter shots and not even realized it. They carry an other-worldly look that feels different from a normally lensed shot. It can be perceived as disorientating as our vision doesn’t work the same way.
The Split Diopter has a clear line down the middle of the frame between foreground and background.
Vertical lines in the frame can be used to hide the shift between foreground and background focus.
Darkness in the frame can also be used to disguise the use of the Split Diopter.
Split Diopters shots can add enhanced hyper-realism to emotional moments.
Robert Wise used the Split Diopter extensively in Star Trek: The Motion Picture.
Steven Spielberg splits the screen in Jaws.
The bottom line is that Split Diopters help achieve the cinematic and story goal of emphasizing subjects as needed by the Director and DP. When utilized for decisive or important moments…they can visually amplify the dramatic tension for the viewer. If used too often, just like with any other technique, the magic of this tool will diminish and the effect will become obvious.
Used sparingly and hidden within the frame…Brian De Palma chose 15 moments in ‘Blow Out’ to bust out the Split Diopter.
Until next time…