ISO 9335:2012

Overview

ISO 9335:2012 - "Optics and photonics - Optical transfer function - Principles and procedures of measurement" provides guidance for constructing and operating equipment used to measure the optical transfer function (OTF) of imaging systems. The standard defines how to set and maintain measuring conditions (the imaging state or I‑state), specifies equipment performance and environmental controls, and lists precautions and correction factors to ensure accurate, comparable OTF measurements. Interferometer‑based instruments are explicitly outside its scope.

Key topics and technical requirements

• Measuring conditions and I‑state: Identify, fix and document all parameters that define the imaging state (focus, spatial frequency range, etc.), so measurements are repeatable and comparable.
• Accuracy and uncertainty allocation: Apportion overall OTF measurement accuracy across contributing parameters (example in the standard: ±0.05 MTF might imply temperature stability of ±1 °C and focal plane setting to ±5 µm).
• Environmental controls: Requirements for temperature, humidity, vibration isolation, air turbulence control, dust and stray light minimization, and mitigation of electromagnetic disturbances.
• Measuring equipment: Sturdy optical bench/plate, accurate mounts and slideways, position scales and gauges, and specified linearity/parallelism tolerances so instrument error stays within measurement accuracy limits.
• System components and layouts: Recommended arrangements for finite and infinite object/image conjugates, on‑axis and off‑axis measurements, use of collimators, auxiliary imaging systems, and rotary‑table setups.
• Test targets and image analysers: Selection and spectral characterization of targets (slits, edges, gratings, apertures); requirement that target spatial frequency spectrum is known to meet measurement accuracy.
• Measurement procedures and data corrections: Procedures for setting conditions, normalizing data, correcting frequency scale and measured modulation, and use of auxiliary imaging systems.
• Presentation and verification: Guidelines for graphical/numeric presentation of OTF data and accuracy checks to validate instrumentation and measurement results.

Applications and users

ISO 9335:2012 is used by:

• Optical and photonics engineers designing or characterizing lenses, cameras, microscopes, telescopes and electro‑optical systems
• Test and calibration laboratories and metrology institutes seeking comparable, reproducible OTF data
• Camera, lens and sensor manufacturers for QA and performance specification
• Research groups and defense/aerospace organizations that require validated imaging performance metrics

Practical benefits include improved inter‑laboratory comparability, clear specification of equipment tolerances, and standardized correction and presentation methods for OTF results.

Related standards

• ISO 9334 - Optics and photonics: OTF definitions and mathematical relationships (normative reference used by ISO 9335)
• ISO 11421 - Referenced for parameters affecting measurement accuracy

Keywords: ISO 9335:2012, optical transfer function, OTF measurement, imaging systems, optics and photonics, measurement procedures, instrument calibration, test target, image analyser.