ISO 13653:2019

This document specifies general optical test methods for the measurement of the relative irradiance in the image field.
This document is applicable to optical imaging systems in the optical spectral region from λ = 100 nm to λ = 1 μm. Theoretical reflections and the comparison with the calculation apply only to optical systems. This document is applicable to rotationally invariant and rotationally variant systems; anamorphic systems, for example, are included.
Telescopic systems are also included. The title of this document refers to the relative irradiance in the image field, but this document is also applicable to determination of the relative radiant power.
NOTE     For telescopic systems, it is suitable to state only the radiant power; for most imaging systems, the conversion from radiant power to irradiance is easy.
As far as measurements are concerned, this document is also applicable to electro-optical systems.
The two methods described differ particularly in the influence of veiling glare.