ISO 70:1981

Overview

ISO 70:1981 - Cinematography - 35 mm negative photographic sound record on 35 mm motion‑picture film - Position and maximum width dimensions - is an ISO International Standard that defines the geometric placement and maximum width tolerances for original monophonic optical soundtracks recorded on 35 mm negative motion‑picture film. It covers both variable area and variable density negative photographic sound records and is intended for original negative materials used in film production and post‑production.

Key topics and technical requirements

• Scope: Specifications apply to original monophonic 35 mm negative photographic sound records (variable area and variable density) on 35 mm film.
• Positioning: Exact lateral placement of the optical soundtrack on the film strip is defined, referenced to a film edge and film travel direction. Precise placement ensures compatibility with optical readers and printers.
• Maximum width and tolerances: The standard sets the maximum permissible width of the negative sound record and associated dimensional tolerances to control crosstalk and alignment with picture and perforations.
• Negative vs. positive track note: ISO 70 explicitly notes that negative sound records have no masking (unlike release print sound tracks), so there is no protection against spurious or noise modulation outside the defined sound area - making correct positioning and width control especially important.
• Reference drawings/tables: Dimensions and tolerances are given in the standard’s figure and table and are linked to related film cutting/perforating and image‑area standards.

Practical applications and users

ISO 70:1981 is used by organizations and professionals involved in:

• Film production and post‑production laboratories that record or process original optical sound negatives.
• Manufacturers of optical soundtrack recorders, scanners, readers and film printing equipment that must align with standardized soundtrack positions and widths.
• Film restoration and archival facilities preserving or duplicating original negative soundtracks.
• Quality control and compliance teams ensuring negative sound records meet dimensional tolerances to avoid audio artifacts during optical playback or duplication.

Using ISO 70 helps prevent alignment errors, reduces noise/crosstalk risks, and ensures interoperability across equipment and facilities handling 35 mm optical sound negatives.

Related standards

• ISO 491 - Cutting and perforating dimensions for 35 mm motion‑picture film.
• ISO 2939 - Picture image area and photographic sound record dimensions for 35 mm release prints.

Keywords: ISO 70:1981, 35 mm negative photographic sound record, variable area, variable density, monophonic, optical soundtrack, sound track dimensions, motion‑picture film.