ISO 26:1993

Overview

ISO 26:1993 is an international standard developed by the International Organization for Standardization (ISO) that specifies the projector usage for 16 mm motion-picture films intended for direct front projection. This third edition updates the previous version from 1985 and provides detailed requirements on the emulsion orientation, projection rate, positioning of the projected image, and the relationship between picture and sound in projectors. It covers both photographic and magnetic sound records as well as silent 16 mm films, ensuring consistent and high-quality film projection in cinema and related fields.

Key Topics

• Emulsion Orientation
  This standard defines the correct position of the film emulsion relative to the light source and lens in projectors. The emulsion orientation depends on the film preparation process and must be clearly indicated by manufacturers to ensure proper projection quality.

• Rate of Projection
  ISO 26 specifies projection frame rates tailored for different film types:

  • For silent films: 16 to 18 frames per second (fps) ±1 fps
  • For sound films: 24 fps ±1 fps
  • Regional adaptations exist, such as 25 fps for TV broadcast areas with 50 Hz power supply.

• Position of Projected Image Area
  The standard mandates precise vertical alignment of the projected image, with the horizontal axis passing through the midpoint between film perforations. Projectors are recommended to incorporate framing adjustments of at least 0.5 mm to fine-tune image positioning.

• Picture and Sound Relationship
  It defines the spatial displacement between the picture frame and the corresponding sound record (either magnetic or photographic) on the film strip. This ensures synchronized audiovisual playback by specifying exact frame differences in line with ISO 490 and ISO 4243 standards.

Applications

ISO 26:1993 is essential for manufacturers and users of 16 mm film projectors, particularly in:

• Professional Cinema Projection
  Ensures compatibility and high fidelity when projecting 16 mm motion pictures with photographic or magnetic soundtracks.

• Educational and Institutional Use
  Facilitates standardized playback quality for training, archival, and museum purposes where 16 mm films are still prevalent.

• Non-professional and Independent Filmmaking
  Guides projection of silent 16 mm films, commonly shot at variable frame rates, maintaining proper image display and sound synchronization.

• Broadcast and TV
  Helps adapt film projection equipment to television standards using specific frame rates suitable for regional power systems.

By adhering to ISO 26, operators guarantee consistent image quality, accurate sound synchronization, and proper functioning of film projectors, reducing equipment incompatibilities and projection errors.

Related Standards

ISO 26 references and complements several important cinematography standards, including:

• ISO 490 – Specifies magnetic sound recording positions and magnetic head gaps for 16 mm film soundtracks.
• ISO 4243 – Details picture image area and photographic sound record dimensions for 16 mm release prints.
• ISO 5768 and ISO 8400 – Provide guidance on film leader specifications and container labeling, supporting correct film handling and projector setup.

Together, these standards create a comprehensive framework supporting the technical consistency and interoperability of 16 mm motion-picture film projection systems worldwide.

Keywords: ISO 26:1993, 16 mm motion-picture films, film projector specifications, emulsion orientation, projection rate, projected image alignment, picture sound synchronization, cinematography standards, 16 mm film projection, magnetic sound film, photographic sound film, direct front projection.