Overview
ISO 7829:1986 - Photography - Black-and-white aerial camera films - Determination of ISO speed and average gradient - defines a standardized method for measuring the ISO speed and the ISO aerial average gradient of black-and-white negative films used in aerial photography. The standard covers film sampling, exposure, handling, sensitometry, processing practices (no single mandatory process), and densitometry. It does not apply to infrared aerial films.
Key topics and technical requirements
- Film–process combinations: ISO 7829 recognizes that a single film can yield different ISO speed and gradient values depending on processing; therefore, the film and the processing conditions must be reported when quoting values.
- Speed determination point: ISO speed is evaluated at a density of 0.30 above base plus fog on the sensitometric curve.
- Average gradient: Defined as the slope between two points on the sensitometric curve (densities separated by 1.00 density unit); the standard gives the method and table-based scale for converting measured values to the ISO aerial average gradient.
- Sampling & storage: Samples must be representative (several batches), stored per manufacturer recommendations and conditioned at 23 ± 2 °C / 50 ± 5% RH prior to testing.
- Exposure & sensitometer: Uses a non‑intermittent illuminance‑scale sensitometer under a defined spectral power distribution (ISO sensitometric aerial daylight) and exposure increments not exceeding specified log10H steps.
- Processing: No mandatory processing is imposed - users should document processing chemistry, times, temperatures, agitation and equipment. Annex A gives an example (D‑19 style) process for organizations that wish to use a standard developer.
- Densitometry: Densities shall be measured with instruments conforming to ISO 5 geometric and spectral requirements; minimum aperture ~7 mm² and readings at least 1 mm from exposure edges.
- Accuracy: Calibration must ensure error in log10 Hm