A split diopter lens is a partial lens that creates striking visual effects in cinematography.
What Is a Split Diopter Lens?
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 to convey a great deal of information or emotional content within a single shot.
How Does a Split Diopter Lens Work?
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.
What Do Split Diopter Lens Shots Convey?
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.
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