Optical front element with two different refractive powers, enabling simultaneous focus at two distinct distances within the same shot.
Technical Details
Split diopters are typically manufactured in strengths from +0.5 to +3 diopters, with +1 and +1.5 diopters being the most commonly used. The diopter half can be ground convex (+) or concave (-). Standard filter sizes range from 77mm to 138mm for professional lenses. The dividing line between the two halves is usually vertical but can be positioned horizontally or diagonally by rotating the filter mount. High-quality split diopters use multi-coated glass to minimize reflections.
History & Development
Brian De Palma popularized the split diopter in the 1970s, after cinematographer Vilmos Zsigmond prominently used the technique in "McCabe & Mrs. Miller" (1971). The technique evolved from macro photography, where split close-up lenses were already used in the 1960s. Manufacturers like Tiffen and Schneider Optics began mass production of dedicated split diopters for film cameras starting in 1972.
Practical Use in Film
De Palma's "Carrie" (1976) features classic split diopter shots, such as when Carrie's face in the foreground and her mother in the background are both in sharp focus simultaneously. Paul Thomas Anderson used the technique in "Boogie Nights" (1997) for phone conversations, where both participants appear sharp in different planes of focus. The split diopter replaces complex focus pulls and reduces the number of necessary cuts. A disadvantage is the visible blur zone along the dividing line, which must be skillfully concealed through image composition.
Comparison & Alternatives
Unlike conventional close-up lenses (+ diopters) that affect the entire image field, the split diopter only acts on one half of the image. Modern alternatives include digital post-production with separate focus planes or deep-focus lenses with extreme depth of field. Tilt-shift lenses offer similar creative possibilities but require precise mechanical adjustment. While digital compositing methods are more flexible, only the optical split diopter creates the characteristic image aesthetic with its hard focus separation in real-time.