Overview
ISO/TS 20490:2024 is a technical specification for measuring autofocus (AF) repeatability of sharpness and latency in digital still cameras. It defines test procedures, apparatus, and reporting methods to determine whether a camera system consistently produces sharp images within a repeatable time frame. The scope is limited to tests using stationary charts (moving-chart tests are excluded). The document is complementary to ISO 15781 and extends AF assessment by combining measured AF latency with objective sharpness metrics.
Key topics and technical requirements
- Scope and intent: Measure the repeatability of AF latency and image sharpness using output images from the camera under test. Tests target both single autofocus (AF‑S) and continuous autofocus (AF‑C) modes.
- Test environment: Nominal conditions include controlled temperature (23 °C ± 3 °C) and defined lighting/illumination for charts.
- Device settings: Cameras are tested in default out‑of‑box settings unless otherwise stated; any deviations must be reported.
- Apparatus & setup:
- Reflective test charts (transmissive charts allowed with caveats)
- Close and far distance charts, actuated holder to insert/remove close chart within ≤ 0.1 s
- Illumination, baffles to control stray light, LED timing panel and computer-controlled capture timing
- Camera holder aligned so optical axis is perpendicular to charts
- Test distances: Recommended close distance = 10× the lens 35 mm equivalent focal length; far distance = 7× close distance (use closest possible focus if 10× not achievable).
- Test charts & content: Supports a range of chart types - high/low contrast, natural images, artificial charts, texture/SFR charts (e.g., ISO 12233), and even 3D scenes - provided the target is stationary and has reasonable information content.
- Sharpness and AF measurement:
- Uses objective sharpness estimation (algorithm details in Annex B)
- Includes defined capture sequences for AF‑C and AF‑S (timing, repetitions)
- Reporting and visualization guidance (result figures, metrics, repeatability analysis)
- Supplementary material: Annexes cover test setup diagrams, sharpness algorithms, human reaction time data (Annex C), and correlation between subjective sharpness and objective scores (Annex D).
Applications and users
This standard is valuable for:
- Camera and smartphone OEMs - R&D validation of AF algorithms and quality assurance prior to release
- Test laboratories and certification bodies - repeatable benchmarking and performance comparison
- Product review labs and reviewers - objective AF performance metrics for comparisons
- Imaging researchers - methodical evaluation of AF behavior under controlled conditions
Practical uses include device benchmarking, tuning AF algorithms, validating marketing claims about focus speed/consistency, and investigating autofocus failures or regressions.
Related standards
- ISO 15781 - Measuring shooting time lag and shutter release time lag (complementary timing tests)
- ISO 12233 - Spatial frequency response (SFR) charts and sharpness metrics
- ISO/TS 19567-2 - Texture charts and related sharpness evaluation methods
Keywords: ISO/TS 20490:2024, autofocus repeatability, AF latency, sharpness measurement, camera testing, AF‑C, AF‑S, SFR, ISO 15781, ISO 12233.