Diffraction Losses in Radiometry and Photometry

Abstract

The precision of radiometry and photometry is reaching a stage, in standardizing laboratories at least, where greater attention should be paid to losses of flux by diffraction. Otherwise errors of up to 0.5% or more may occur. This article reviews from the radiometric point of view diffraction losses at circular apertures, for both the Fraunhofer and Fresnel conditions and for both monochromatic and complex radiation. Where tedious calculations are required to evaluate the exact expression for the diffraction loss, special emphasis is placed on approximate relationships.