ISO 14490-6:2014

Overview

ISO 14490-6:2014 - Optics and photonics: Test methods for telescopic systems - Part 6: Test methods for veiling glare index - specifies laboratory procedures to determine the veiling glare index (VGI) of telescopic systems and observational telescopic instruments. The standard adopts the black patch (integral) method (as described in ISO 9358:1994) for terrestrial telescopes and defines the measurement principle, required test arrangement, procedure, presentation of results and repeatability criteria.

Key topics and technical requirements

• Measurement principle: VGI, S = E1 / E2, is the ratio of illuminance of the image of a black surface (E1) within a diffusely illuminated white field to the illuminance of the image of a totally white surface (E2). Results are expressed as a percentage.
• Preferred method: Black patch (integral) method for telescopic systems; glare spread function is referenced for astronomical use to ISO 9358:1994.
• Test arrangement components:
  • Integrating sphere (diameter ≥ 15× entrance pupil, min. 1 m), interior reflectance ≥ 85% across 380–780 nm.
  • Object-side collimator: achromatic lens, min. f-number 10, aperture > 1.2× objective lens diameter; focal length equals sphere interior diameter; antireflection coatings required.
  • Measurement & evaluation unit: limiting stop (8 mm at exit pupil), filter (to match detector to photopic response), image-side collimator, measuring stop (20–50% of black image diameter), radiation detector and indicator.
  • Reference surfaces: removable white disk and annular black element with light trap (black trap luminance < 0.1% of sphere interior).
• Light source: stable radiant flux (≤1% variation during paired measurements) approximating black-body 2 800–3 200 K.
• Procedure: clean optics, align test specimen close to object-side collimator, measure white image illuminance then black image illuminance; for off-axis tests slew around entrance/exit pupils and test points at 0.5 and 0.7 of half field of view (take maximum for non-rotationally symmetric systems).
• Results & reporting: tabular and graphical presentation (S to one decimal), repeatability relative error ≤ 10%; test report per ISO 14490-1:2005 Clause 13.
• Informative annex: Annex A covers determination of luminance ratio of black reference to sphere interior.

Applications and who uses it

• Optical engineers and designers validating stray light and contrast performance of telescopic sights, binoculars, spotting scopes and other telescopic systems.
• Test laboratories performing acceptance, R&D and quality control measurements for manufacturers.
• Procurement, compliance and certification teams assessing optical instrument performance for military, surveillance, marine, and outdoor imaging applications.
• Researchers studying stray light, veiling glare and human visual contrast in telescopic systems.

Related standards

• ISO 9358:1994 - Veiling glare definitions and measurement methods (general)
• ISO 14132-1 - Vocabulary for telescopic systems
• ISO 14490-1:2005 - Test methods for basic characteristics of telescopic systems

Keywords: ISO 14490-6:2014, veiling glare index, telescopic systems, test methods, integrating sphere, black patch method, optics and photonics, measurement setup.