Overview
ISO 14490-7:2016 - "Optics and photonics - Test methods for telescopic systems - Part 7: Test methods for limit of resolution" defines standardized procedures to measure the limit of resolution of telescopic systems and observational telescopic instruments. The standard specifies test arrangements, required test equipment, measurement procedures, calculation methods and reporting requirements to determine the minimum angular separation at which adjacent bars in a bar‑type resolution target can be distinguished.
Key topics and technical requirements
- Test concept: Uses a bar‑type resolution test target placed at the focal plane of a collimator to produce a collimated image for the test specimen (telescope or observational instrument).
- Resolution definition: The limit of resolution is the minimum angular distance between centrelines of adjacent bright (or dark) bars that can be detected through the test specimen.
- Essential equipment & setup:
- Collimator lens with diameter ≥ 1.2 × entrance‑pupil diameter of the test specimen and focal length ≥ 5 × objective focal length.
- Bar‑type resolution test target (glass plate with vertical, horizontal and ±45° patterns) mounted at the collimator focal plane.
- Uniform illumination (correlated colour temperature 5 000–6 000 K; mean illuminance uniformity ±5% Peak-to‑Valley).
- Optional auxiliary telescope; magnification must not reduce the system exit pupil below 0.8 mm. Guidance given when auxiliary telescope is unnecessary (e.g., angular limit worse than 2′–3′ and exit pupil