ISO 11421:2025

Overview

ISO 11421:2025 - Optics and photonics - Uncertainty of optical transfer function (OTF) measurement provides guidance for evaluating and reporting the measurement uncertainty associated with Optical Transfer Function (OTF) test equipment. The standard focuses primarily on the Modulation Transfer Function (MTF) component of OTF (main body) and addresses the Phase Transfer Function (PTF) in Annex A. It describes sources of error, methods to assess those errors, procedures for calculating overall uncertainty, and approaches for specifying a general equipment uncertainty.

Key Topics

• Sources of uncertainty in OTF measuring systems (geometry, alignment, stray radiation, spectral characteristics, detector linearity, coherent radiation, baseline error, residual aberrations).
• Optical bench geometry and alignment: slide straightness, parallelism, rotation-angle errors, image-distance setting and collimation.
• Spatial and spectral errors: spatial frequency errors, slit-width and field-angle corrections, off-axis magnification and distortion effects.
• Data and signal processing: impact of processing algorithms and measurement chain on uncertainty.
• Assessment and calculation: methods for assessing individual error contributions, combining them to calculate overall measurement uncertainty in line with ISO/IEC GUM and VIM principles.
• Specification of equipment uncertainty: Nominal Uncertainty Value (NUV), plus categories such as Standard-Lens Measurements (SLM), Audit-Lens Measurements (ALM), and Slit Aperture Test (SAT).
• Routine performance evaluation and recommended checks to maintain measurement reliability.
• Supporting material: Annex B (rate of change of MTF vs parameters) and Annex C (example NUV calculation).

Applications

ISO 11421:2025 is intended for:

• Optical and photonics engineers performing objective image-quality testing.
• Lens manufacturers and designers validating MTF performance.
• Calibration and metrology laboratories establishing OTF measurement capabilities and uncertainty budgets.
• Camera and imaging-system integrators verifying imaging performance for specifications and QA.
• Researchers studying imaging-system characterization and measurement reproducibility.

Practical uses include specifying measurement uncertainty for test equipment, improving repeatability of MTF/OTF testing, auditing lens performance, and documenting measurement confidence for product specifications and compliance.

Related Standards

• ISO 9334 - Terminology for OTF/MTF
• ISO 9335 - Principles and procedures for OTF measurement
• ISO 9336 (parts) - Application-specific OTF measurement
• ISO/IEC Guide 98 (GUM) and ISO/IEC Guide 99 (VIM) - Measurement uncertainty and vocabulary

Keywords: ISO 11421, OTF measurement, MTF uncertainty, optical transfer function, measurement uncertainty, optics and photonics, standard lens, Nominal Uncertainty Value.