Distinction between image magnification and irradiance magnification: a commentary

Abstract

We take a closer look at the transverse magnification factor m in Eqs. (4) and (7) in a recent paper by Reshidko and Sasian and suggest that a distinction be made between the square of the “first-order transverse magnification” and the “magnification of the irradiance.” When applied to image irradiance calculations, the former quantity is restricted to aberration-free lenses, whereas the latter is not. For realistic lenses (i.e., lenses whose aberrations are not totally zero, but function sufficiently well), as might be expected, these two magnification quantities are generally not equal, except in the limit of low numerical aperture.