Overview
ISO 9342-1:2023 - Optics and optical instruments - Test lenses for calibration of focimeters - Part 1: Reference lenses for focimeters used for measuring spectacle lenses - defines the requirements and verification method for reference lenses used to calibrate and check focimeters that measure spectacle form lenses (for example, those complying with ISO 8598-1). The standard covers design, materials, verified-power determination and marking, and gives guidance for spherical, prismatic, cylindrical and spherocylindrical reference lenses and neutral density reference filters.
Key topics and technical requirements
- Scope and purpose
- Calibration and verification of focimeters used for spectacle lens measurement.
- Defines the concept of verified power: a calculated back vertex power derived from measured lens parameters with stated uncertainty.
- Materials and workmanship
- Reference lenses are normally made of homogeneous white crown glass, free of bubbles/striae within an 8 mm radius of the aperture; other materials allowed if equivalent stability and uncertainty are demonstrated.
- Reference wavelengths
- Verified powers are reported for a stated reference wavelength: green mercury e-line (λ = 546.07 nm) or yellow helium d-line (λ = 587.56 nm) per ISO 7944.
- Spherical reference lenses
- Recommended nominal set: −25 D, −20 D, −15 D, −10 D, −5 D, +5 D, +10 D, +15 D, +20 D, +25 D.
- Aperture ≥ 15 mm; back-surface curvature and centre thickness chosen to mimic spectacle lens form to limit spherical aberration.
- Example maximum uncertainties on verified spherical power (standard set) range from ±0.01 D to ±0.04 D depending on nominal power (values specified in Table 1 of the standard).
- Optional low-power set (e.g., ±0.12 / ±0.25 / ±2.5 D) with tighter uncertainty (example ±0.01 D) for validating automated focimeters.
- Prismatic, cylindrical and spherocylindrical lenses
- Prismatic reference lenses: plane optical surfaces, aperture ≥ 15 mm. Recommended prism powers: 2 Δ, 5 Δ, 10 Δ, 15 Δ, 20 Δ. Uncertainties and validation methods are detailed (see Annex B).
- Cylindrical and spherocylindrical designs and validation procedures are covered to verify axis and non-symmetric cylinder measurements (Annexes B and C).
- Traceability and marking
- Parameters used to compute verified power (refractive index, radii, thickness) must be measured using procedures or equipment traceable to accredited metrology laboratories (e.g., ISO/IEC 17025). Recommended protective mounts should be marked with the verified power and reference wavelength.
Applications and who uses this standard
- Calibration and periodic verification of focimeters in:
- Ophthalmic instrument manufacturers
- Metrology and calibration laboratories
- Optical dispensaries and eyewear quality-control facilities
- Research labs developing lens measurement equipment
- Useful for instrument technicians, calibration service providers and optical engineers responsible for ensuring measurement accuracy of spectacle lens power, prism and axis.
Related standards
Keywords: ISO 9342-1:2023, focimeter calibration, reference lenses, back vertex power, verified power, spectacle lenses, prismatic reference lens, spherical reference lens, calibration standards.
Open preview (PDF)Optics and optical instruments — Test lenses for calibration of focimeters — Part 1: Reference lenses for focimeters used for measuring spectacle lenses