Optical glass that refracts and redirects light — creates mirror effects, double images, or hides the camera behind objects. Staple in thrillers and psychological drama.
The prism is one of the more subtle optical tools we employ on set to manipulate perspective and perception—without having to pan the camera. A three-sided glass element that refracts and redirects light rays allows us to simultaneously capture two or more spatially separated scenes within a single frame, or to hide the camera behind objects that would otherwise block its viewpoint.
In practical application, we mount the prism directly in front of the lens or as a specialized attachment lens. A classic use case: we position the camera seemingly head-on to an actor, but the prism refracts a side view into the frame—thus, the viewer simultaneously sees the frontal view and what is happening beside the camera. This creates a disturbing simultaneity, particularly effective in psychological thrillers where we want to visualize the fragmentation of perception. For split screens, we work with two prisms in combination: the first reflects an image onto the second, which then directs it into the lens—effectively showing two scenes superimposed.
The technical disadvantage is light loss—depending on the quality and coating of the prisms, we lose 15 to 30 percent of the incident light. This requires us to either open the aperture wider or use additional lighting. This is less critical with LED sets, but with available daylight, we must calculate carefully. Image quality is also affected—reflections, slight vignetting, color fringing—which is why we opt for premium materials from specialized camera suppliers, not cheap attachment lenses from a photo shop.
Psychological films and experimental works love prisms; suspense sequences utilize the unexpected spatial break to build tension. We also use them in music videos or montages to depict temporal or sensory desynchronization. Important: the prism is not a gimmick—it must have a narrative function. Anyone who uses it solely for its effect will be noticed by everyone in the audience.