ISO 2240:2003

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 < 0.05.
• Marking: Report as e.g. ISO 100, ISO 21°, or ISO 100/21°.

Applications and who uses it

ISO 2240:2003 is aimed at:

• Film manufacturers and QA labs for product certification, batch testing and labeling of colour reversal films.
• Sensitometry and densitometry labs establishing ISO speed for new film emulsions or process variants.
• Camera and exposure‑meter manufacturers referencing standardized film speed to calibrate automatic exposure controls (see ISO 2721 and ISO 2720).
• Photographic testing services and technical documentation teams producing exposure guidance for slide projection and transparency viewing.

Practical benefits include consistent exposure recommendations, reliable inter‑lab comparisons, and standardized product marking for marketing and user guidance.

Related standards

Relevant references for implementation and measurement:

• ISO 5‑2, ISO 5‑3 (densitometry conditions)
• ISO 7589 (sensitometry illuminants)
• ISO 2720, ISO 2721 (exposure meters & camera controls)
• ISO 3664 (viewing conditions)
• ISO 2910 (screen luminance for projection)

Keywords: ISO 2240:2003, colour reversal camera films, ISO speed determination, sensitometry, densitometry, exposure, film speed, transparency, slide film, 8 mm, 16 mm.