ISO 25178-606:2026

Overview

ISO 25178-606:2026 is an international standard developed by the International Organization for Standardization (ISO) as part of the ISO 25178 series on Geometrical Product Specifications (GPS) for surface texture measurement. This document defines the design and characteristics of non-contact focus variation (FV) instruments used for areal surface texture measurement. Focus variation instruments provide precise three-dimensional topographical data, applicable for both areal and profiling surface measurements, especially in quality control and metrology settings. This standard applies to focus variation techniques with fixed or no pattern illumination, excluding varying pattern illumination methods.

Key Topics

• Focus Variation Principle: Focus variation is an advanced optical measurement technique that determines surface topography by analyzing a sequence of captured images at different focal positions. The sharpness of each image indicates the precise surface height at each lateral position.
• Instrument Components: An FV instrument consists of key components such as an electronic camera, optics, white light source, optional ring lights, polarizers and analyzers (for polarization mode), axial scanner, and data processing algorithms.
• Illumination Systems: FV instruments can use various illumination systems, including coaxial, ring light, and fixed pattern projection, to enhance measurement capability across different surface types.
• Measurement Algorithms: Dedicated algorithms process focus information curves to calculate surface heights, using focus measures like image sharpness, often enhanced through curve-fitting techniques for improved accuracy.
• Metrological Characteristics: In accordance with ISO 25178-600, critical measurement parameters include topographic spatial resolution, linearity deviation, flatness deviation, measurement noise, and maximum measurable slope.
• Sources of Error: The standard identifies influence quantities affecting measurement accuracy, including light source properties, numerical aperture, instrument noise, environmental vibrations, optical resolution, sampling interval, and optical distortion.

Applications

• Industrial Quality Assurance: Focus variation instruments are widely used in precision industries such as automotive, aerospace, medical devices, and semiconductor manufacturing for areal surface texture measurement and profile assessment.
• Non-Destructive Testing: As non-contact, FV methods enable detailed analysis of delicate or finished components without risk of surface damage.
• Material Research: Researchers employ focus variation instruments for studying material properties, wear analysis, and surface functional performance by capturing detailed 3D topography.
• Calibration and Verification: The standard informs procedures for calibrating and verifying FV instruments to ensure consistency with globally recognized metrological practices.

Related Standards

ISO 25178-606:2026 builds upon and references several related standards, ensuring compatibility and consistency within the ISO GPS framework:

• ISO 25178-600: Specifies metrological characteristics for areal surface topography measuring methods.
• ISO 14638: Provides an overview of the ISO GPS system and matrix model.
• ISO 8015: Outlines the fundamental rules for GPS.
• ISO 14253-1: Details decision rules for the verification of conformity to specifications.
• ISO 25178-700 & ISO 12179: Cover calibration, adjustment, and verification methods for surface texture measuring instruments.

Practical Value

Adopting ISO 25178-606:2026 ensures that manufacturers and laboratories use standardized methods when selecting, designing, and calibrating focus variation instruments. This supports reliable, repeatable, and comparable areal surface texture measurements across global supply chains. The standard’s guidelines help mitigate measurement errors, enhance product quality, and streamline conformance to international requirements for surface topography.

Keywords: ISO 25178-606, focus variation instruments, areal surface texture, non-contact measurement, optical metrology, surface topography, GPS, instrument calibration, surface profiling, industrial quality assurance.