ACCURATE CALCULATION OF THE IRRADIANCE OF OPTICAL-IMAGES

Accurate knowledge of the relative image irradiance is important in th e design of some optical instruments, e.g., IR systems, where it deter mines the apparent temperature of the object, and camera systems emplo ying irregular-shaped aperture stops or light-absorbing elements. We r eview the quick Hopkins method for calculating the relative image irra diance of systems with circular or elliptical stops and then describe a modification that enables it to be used for the less conventional sy stems mentioned. The new method is used to calculate the relative irra diance of a camera objective that includes a neutral density wedge. We also present a brief discussion of the often misunderstood cos(4) law , which is of some importance in the design of optical instruments. (C ) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091-3286 (98)00910-6].