Overview
ISO 5800:1987 is an international standard developed by the International Organization for Standardization (ISO) that specifies the method for determining the ISO speed of colour negative films used in still photography. This standard is essential for photographers, film manufacturers, and imaging professionals to ensure consistent and reliable film sensitivity measurements. The scope applies primarily to colour negative films used for producing reflection-type colour prints, although it also covers films for creating colour transparencies. It explicitly excludes colour negative films designed for motion picture or aerial photography.
The standard ensures that ISO speed values are determined using uniform exposure, processing, and densitometry conditions, facilitating accurate comparison and practical application in photographic exposure settings.
Key Topics
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ISO Speed Definition
The ISO speed represents a quantitative measure of a film’s response to luminous energy under specified conditions of exposure, processing, and analysis. It enables photographers to select suitable exposure settings and helps manufacturers maintain quality control.
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Sampling and Storage
Films must be stored under controlled conditions simulating typical aged use before evaluation to reflect realistic photographic results. Multiple batches are tested for representative calibration.
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Exposure Conditions
Exposure is measured in lux seconds with specific sensitometers and illuminants complying with ISO 7539. The standard defines exposure values in one exposure value unit (Ev or Eₙ) increments, linked to doubling or halving light exposure.
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Processing Parameters
Film processing following exposure must adhere to recommended temperature (23 ± 2 °C) and humidity (50 ± 5 %) conditions. Processing times vary between general-purpose and professional films, but specific chemical formulations are left to manufacturers.
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Densitometry and Evaluation
Diffuse transmission densities are measured using densitometers under geometric and spectral conditions complying with ISO 5-2 and ISO 5-3, respectively. Sensitometric curves for red, green, and blue channels are plotted against logarithmic exposure values to calculate film speed.
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Speed Calculation and Classification
The standard outlines formulas for both arithmetic and logarithmic speed calculations. The ISO speed is ultimately rounded and presented in a format such as ISO 100/21°, indicating standard sensitivity under defined conditions.
Applications
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Photography Exposure Control
ISO 5800 provides photographers with a reliable basis for exposure meter calibration and camera exposure settings, particularly for film-based still photography.
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Film Manufacturing & Quality Assurance
Film producers use this standard to calibrate and certify film speed, ensuring conformity with international norms and consistent film performance.
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Film Testing & Calibration Labs
Laboratories conducting sensitometric analysis rely on ISO 5800 to perform standardized speed tests, enabling accurate product classification and comparison across different film types.
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Camera Cartridge Design
Some camera cartridge systems exploit the overexposure latitude defined in the standard to improve usability under varying lighting conditions, enhancing photographic outcomes in consumer cameras.
Related Standards
- ISO 2720 – General-purpose photographic exposure meters (photoelectric type) – Guide to product specification
- ISO 2721 – Cameras – Automatic exposure control
- ISO 7539 – Illuminants for sensitometry – Specifications for daylight and tungsten light sources
- ISO 554 – Standard atmospheres for conditioning and testing photographic materials
- ISO 7599 – Photography – Illuminants used for sensitometric exposure
- ISO 5-2 – Photography – Densitometry – Geometrical conditions
- ISO 5-3 – Photography – Densitometry – Spectral conditions
ISO 5800:1987 remains a foundational standard for determining the ISO speed of colour negative films in still photography, crucial for maintaining consistency and reliability in photographic exposures and film sensitivity ratings worldwide.