Split Diopter Lens Explained: 4 Split Diopter Shots in Cinema

A split diopter is a partial lens that attaches to a standard camera lens and features at least two different focal planes. This lens attachment has the effect of greatly expanding the depth of field so that the immediate foreground and the distant background can both be in sharp focus. In filmmaking, this allows the cinematographer to convey a great deal of information or emotional content within a single shot.

A split lens diopter, also known as a split-field diopter or a split focus diopter, is an adapter that works by adding a convex section to a standard camera lens filter to refocus the light traveling through the convex portion. When this light hits the film or sensor in the camera, that section of the image will be on a different focal plane than the rest of the picture, allowing both foreground and background to be sharply in focus at the same time.

Technically, a split diopter creates the illusion of deep focus. The two different planes of focus combine into a single image. Some diopters work as a close-up lens, allowing anamorphic lenses, which can’t focus on objects too close to the lens, to see those objects clearly. Because the two planes of focus are separate, there will be a border between them, often appearing as a blurred vertical line in the center of the image where the convex element ends. Filmmakers can disguise this to some degree, but it is challenging to hide completely.

Cinematographers can use split diopter lenses to create different visual effects to achieve the emotional or narrative impact desired by the director. Split diopter lenses can make the following:

• Complex compositions: By creating a deep depth of field, the director can compose a scene that will convey a lot of information and texture into a single shot. Both the extreme foreground and the distant background can be in focus, so tiny details and grand dimensions can appear simultaneously, offering the viewer a degree of choice in where to focus their eyes.
• Stark juxtaposition: Many split diopter shots will feature one character’s face in close-up while the rest of the scene, perhaps including an additional character, play out in the background. This can emphasize the character’s reaction to an event or underline their emotional state as the scene unfolds.
• Under pressure: Ironically, the exact mechanism that creates an illusion of depth can also create flatness. Because the split focus effect doesn’t mimic the way our eyes naturally process visual information, scenes using this technique can seem unnatural and create a sense of claustrophobia. In some cases, the split diopter can make a character look like their surroundings are squeezing them.

The split diopter lens adapter has long been a trusty tool in the cinematographer’s camera accessories kit. Some notable examples of its use include:

1. 1. Citizen Kane (1941): Orson Welles’s debut feature was heavily reliant on camera effects. Along with his cinematographer Gregg Toland, he pushed the use of deep focus in daring new directions, relying on various sophisticated film-printing and camera techniques, including the split diopter. In a few scenes, a character’s head is sharply in focus in the foreground while other characters across the room are also in focus⁠—this was accomplished with a split-plane diopter, among other tools.
2. 2. West Side Story (1961): Robert Wise and Jerome Robbins co-directed this adaptation of the Broadway musical and used cinematography techniques to heighten the emotions. In one sequence, the focus during a community dance shifts, isolating the main characters as they lock eyes from across the room and approach each other. The effect of each character seeing only the other, with the rest of the scene fading to a blur, was achieved with diopter lenses.
3. 3. Blow Out (1981): The 1970s and ’80s saw heavy usage of the split diopter lens effect, and director Brian De Palma was one of its most avid exponents. Several shots in Blow Out, which stars John Travolta as a sound recordist who becomes involved in a conspiracy plot, use the effect to ratchet up the suspense and show the character’s increasing paranoia. De Palma also used split-diopter effects throughout several of his other films, such as Carrie (1976) and The Untouchables (1987).
4. 4. Reservoir Dogs (1992): Quentin Tarantino’s admiration for 1970s American cinema is evident in his use of split diopter effects, several of which appear in his debut film. In one scene, an exchange between a captured police officer and a severely wounded criminal (played by Tim Roth) plays out using a split diopter.

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