Running film through camera multiple times to layer exposures — each pass adds a new element. Classic in-camera technique; analog gold, rarely done now.
You take an already exposed film back into the camera and run it through again — each time with new lighting, new composition, or new objects in front of the lens. The result: multiple images are superimposed on the same film frame. Classic special effect photography, which is almost extinct today, but still unfolds its full power in analog work or deliberately artisanal productions.
The practice requires exact control. Each pass must be photographically calibrated — too bright and the first layer will wash out, too dark and the second will become invisible. You need precise exposure metering for each layer, often reduced by at least one stop from normal exposure. After the first pass, the film is stored in the dark, then reloaded — and here lies the biggest pitfall: perforation accuracy. Even minimal misalignments lead to image jitter or double outlines. Some camera technicians work with markings on film spools or special rewinding techniques to ensure frame alignment.
On set, this was the standard tool for ghost appearances, doppelgangers, or psychological effects — think of the superimpositions in classic horror or avant-garde film. You plan each pass visually beforehand, sketching the composition and lighting of each layer, because changes during exposure are impossible. Digital post-production compositing has made this obsolete today, but the optical character — the slight halo effect, the blending quality — is irreplaceable and can only be imperfectly replicated digitally.
For modern productions, it is only relevant today for intentional analog aesthetics or experimental cinema. Some DPs consciously resort to this technique to create artificiality where digital appears too perfect. The challenge remains: you need patience, exact planning, and absolute care when handling the material — a single scratch or a smudge between passes cannot be repaired. But it is precisely this irreversibility that creates the artistic focus that digital workflows have lost.