Overview
ISO 491:2002 - Cinematography: 35 mm motion-picture film and magnetic film - Cutting and perforating dimensions defines the physical cutting and perforating geometry for unexposed 35 mm motion-picture film and 35 mm magnetic film. The standard specifies dimensional tolerances, perforation types (Type P, Type N, Type DH), measurement conditions and pitch definitions used for camera, intermediate and print films. It includes normative metric dimensions (Table 1), an inch-equivalent Annex, and informative guidance on stability and manufacturing practice.
Key topics and technical requirements
- Dimensional tolerances and examples: critical dimensions are specified at the time of cutting/perforating (measured at (23 ± 1) °C and (50 ± 5) % RH). Examples from the standard:
- Overall film width (A) = 34.975 ± 0.025 mm
- Perforation pitch (B) = 4.75 ± 0.01 mm (long pitch)
- Short pitch (B') = 4.74 ± 0.01 mm (where applicable)
- Length of any 100 consecutive intervals (L) = 475.00 ± 0.38 mm
- Perforation types: Type P, Type N and Type DH are defined with differing hole shapes, radii and positions; current practice favors Type P for print films and Type N for some camera/intermediate uses, with a long‑term goal toward universal Type P.
- Measurement conditions: Dimensions are valid at specified reference atmosphere (ISO 554). Calibration of measuring instruments referenced to 20 °C.
- Dimensional stability and low-shrinkage film: Annex B defines low-shrinkage film (≤ 0.2 % shrinkage under a defined sequence of storage, exposure and processing) and discusses shrinkage/swelling effects due to temperature, humidity and chemical loss.
- Pitch selection guidance: Guidance on choosing long vs short pitch (B vs B') for printing processes - typical pitch differential for printing sprocket contact is about 0.3 % (±0.1 %) to account for film thickness and sprocket curvature.
Applications and users
ISO 491 is practical for:
- Film manufacturers cutting and perforating 35 mm photographic and magnetic stock.
- Post-production and printing houses ensuring compatibility between originals and release prints.
- Camera, printer and projector equipment designers who must match sprocket geometry and pitch for reliable film transport.
- Film labs, archives and restorers managing dimensional stability, shrinkage classification and archival handling.
- Standards bodies and quality managers enforcing interchangeability and cross‑platform compatibility for 35 mm workflows.
Keywords: ISO 491:2002, 35 mm motion-picture film, perforation, cutting dimensions, magnetic film, film pitch, Type P perforation, low-shrinkage film, dimensional stability.
Related standards
- ISO 554 - Standard atmospheres for conditioning and/or testing (reference climate)
- ISO 18906 - Imaging materials - Photographic films - Specifications for safety film
- (Bibliography) ISO 1 - Standard reference temperature for geometrical product specifications
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