title: Maréchal intensity formula for small-Fresnel-number systems.
abstract: A simple modification of the known Maréchal intensity formula is proposed. It enables one to evaluate the near the-diffraction-focus intensity distribution for well-corrected optical systems with small Fresnel numbers of the focusing geometry. As an example, the focal-shift effect in perfect systems is briefly reexamined.
authors.forename: S
authors.initials: S
authors.lastname: Szapiel