Overview
ISO 2240:2003 specifies the standardized method for determining the ISO speed of colour reversal camera films (slide/transparency films). It applies to continuous‑tone pictorial films intended for viewing on transparency illuminators or by projection, and to 8 mm and 16 mm motion‑picture films used in non‑professional applications. This edition replaces ISO 2240:1994 and defines how to measure and report film speed so that exposure meters, camera automatic exposure systems and users can obtain predictable results.
Key topics and technical requirements
- Scope: Colour reversal (positive) films for transparencies and non‑professional 8/16 mm motion‑picture films; not for professional motion‑picture films.
- Sampling & storage: Test several batches; store samples per manufacturer recommendations to simulate normal user age before testing.
- Environmental conditions: Equilibrate samples at (23 ± 2) °C and (50 ± 5) % RH during exposure and before processing.
- Sensitometry & exposure:
- Use a non‑intermittent, illuminance‑scale sensitometer.
- Use illuminants conforming to ISO 7589 (daylight, tungsten, photoflood). Specify illuminant in instructions.
- Exposure time for speed determination: 5 s to 1/1 000 s (reciprocity effects should be noted).
- If filters are used in-camera, report an “equivalent” speed; ISO speed applies without filters.
- Modulation requirements: Limits on spectral diffuse transmission modulation across 400–700 nm (and 360–400 nm allowances) to ensure uniformity of test exposures.
- Processing:
- Processing procedures are not prescribed - use manufacturer‑recommended processes.
- Timing between exposure and processing: general‑purpose films 5–10 days, professional films 4 h–7 days.
- Film speed is dependent on processing; processing conditions must be reported with quoted speed.
- Densitometry:
- Measure ISO standard visual diffuse transmission density per ISO 5‑2 (geometric) and ISO 5‑3 (spectral).
- Readings in uniform image areas (≥1 mm from edges).
- Evaluation & calculation:
- Plot density vs. log10(H) to obtain a sensitometric curve.
- Define point P at 0.20 above minimum density and point S at 2.00 above minimum density. The slope between P and S should be between −1.4 and −1.8.
- Compute log Hm from H_P and H_S, average log Hm across batches, then convert to ISO speed using the standard scale (Table 1).
- Accuracy: absolute error in log H must be
