Overview
ISO 9848:2003 - Photography - Source document microfilms - Determination of ISO speed and ISO average gradient describes a standardized test method to measure the ISO speed and ISO average gradient of black-and-white camera negative films used for first‑generation microfilming of source documents. The standard is specific to exposures made with an incandescent tungsten illuminant (2 650 K ± 100 K) and is intended to provide practical, comparable values for film/process combinations to be used when computing exposures and selecting microfilm materials.
Key topics and technical requirements
- Scope and exclusions: Applies to first‑generation microfilming of alphanumeric and line documents (books, correspondence, drawings). Excludes pictorial/continuous‑tone reproduction, computer output microfilm (COM), reversal/direct‑positive films and exposures made with non‑tungsten sources (laser, CRT).
- Test principle: Produce a sensitometric curve from exposures and density readings to derive ISO speed and ISO average gradient.
- Radiant energy quality: Use an incandescent tungsten source at 2 650 K ± 100 K, simulating an “undervolted” photoflood (see 5.3.3).
- Exposure time: Must reflect the film’s intended use and be specified because of reciprocity law failure (speed can depend on exposure time).
- Sampling & storage: Evaluate multiple batches and store samples per manufacturer recommendations to represent end‑use age.
- Processing: Process conditions are not prescribed by the standard (film/process systems vary). Manufacturer process specifications should be used when reporting ISO values.
- Densitometry: Measure ISO standard visual diffuse transmission density using instruments compliant with ISO 5‑2 (geometric) and ISO 5‑3 (spectral); readings taken ≥1 mm from exposed edges.
- Handling: Films must be handled in complete darkness for sensitometric exposing and processing (no safelight exposure).
- Modulation and measurement tolerances: The standard defines limits on modulator spectral diffuse transmission variation and exposure step sizes to ensure uniformity of test exposures.
Applications and users
- Primary uses: Comparing film/process combinations, calculating exposure settings, and guiding initial film selection for archival and document microfilming workflows.
- Typical users:
- Film manufacturers and product developers (to publish comparable speed/contrast data)
- Microfilm service bureaus and archival labs (for quality control and exposure setup)
- Photographic test laboratories and equipment manufacturers (sensitometers, densitometers)
- Archivists and records managers selecting microfilm products for long‑term document preservation
Related standards
- ISO 5‑2 - Density measurements (geometric conditions)
- ISO 5‑3 - Density measurements (spectral conditions)
- ISO 554 - Standard atmospheres for conditioning/testing
- ISO 6728 - Camera lens spectral transmittance (ISO colour contribution index)
Keywords: ISO 9848:2003, microfilms, ISO speed, ISO average gradient, tungsten source, sensitometric curve, densitometry, reciprocity law failure, black-and-white camera negative.