ISO 21395-2:2022

Overview

ISO 21395-2:2022 sets out a precise optical test method for measuring the refractive index of optical glasses using the V-block refractometer method. Developed by ISO (International Organization for Standardization), this standard is designed for application within the wavelength range of 365 nm to 2400 nm, with a measurement accuracy within 3 × 10⁻⁵. While this method may be used for some non-glass materials, its development and validation focus specifically on optical glass.

This method presents a practical alternative to the minimum deviation method (covered in ISO 21395-1), offering a less complex and faster approach for quality control and characterization of optical glass in industrial and laboratory settings. The V-block refractometer method supports accurate communication and quality assurance between glass manufacturers and optical component producers.

Key Topics

• Test Principle: Utilizes the deviation of a light beam passing through a specimen supported by a V-block prism, allowing calculation of the refractive index by measuring the deviation angle.
• High Precision Measurement: Ensures refractive index results accurate to within 3 × 10⁻⁵, essential for optical applications demanding high precision.
• Measurement Equipment: Specifies the configuration and tolerances for equipment, including:
  • V-block prism with specific angular and surface quality requirements
  • Reference blocks, matching liquids, light sources, bandpass filters, collimator lens, and telescopes
  • Detectors (OR human eye) and deviation angle measurement devices.
• Environmental Controls: Highlights the importance of controlled temperature (20°C to 25°C) and atmospheric pressure (86 kPa to 106 kPa) during measurement for consistency and accuracy.
• Specimen Preparation: Addresses requirements for specimen shape, apex angle, and contact surfaces to ensure optimal measurement conditions.
• Reporting Requirements: Specifies key data to be included in the test report for traceability and reproducibility.

Applications

The V-block refractometer method covered in ISO 21395-2:2022 is widely applicable in:

• Optical Glass Manufacturing: Supporting routine quality assurance and specification verification for various types of optical glasses.
• Optical Component Production: Allowing lens and prism manufacturers to precisely match refractive indices for optimal performance in optical systems.
• Research and Development: Facilitating scientific studies and development of new glass types by enabling straightforward, accurate refractive index measurement.
• Incoming Material Quality Checks: Empowering organizations to quickly assess and compare the refractive indices of supplied glass batches.
• Calibration Reference: Useful as a reference procedure for calibrating other refractive index measurement tools.

Related Standards

For a comprehensive approach to the measurement and specification of optical glass properties, consider these relevant ISO standards:

• ISO 21395-1 – Optics and photonics – Test method for refractive index of optical glasses – Part 1: Minimum deviation method
• ISO 9802 – Raw optical glass – Vocabulary
• ISO 280 – Essential oils – Determination of refractive index (for refractive index matching liquids)
• ISO 80000-1 / ISO 80000-3 – Quantities and units (for units and terminology in measurement)

Practical Value

Adopting ISO 21395-2:2022 ensures that organizations in the optics and photonics sectors can:

• Achieve consistent, repeatable refractive index measurements using standardized procedures.
• Minimize ambiguity in test results, facilitating clear communication across the supply chain.
• Increase measurement throughput during routine quality checks, thanks to the practical and less demanding nature of the V-block method.
• Maintain compliance with international best practices in optical glass characterization, supporting both production efficiency and global trade requirements.

By implementing this standard, engineers and technicians can rely on robust, validated metrology-crucial for the continuous improvement and reliability of advanced optical systems.