title: Photometric error analysis, x: enriched energy (total illuminance) calculations for annular apertures.
abstract: Encircled energy calculations show the effects of focus errors, spherical aberration, and a central stop on image contrast. The complementary quantity (excluded energy) gives the illumination at the center of a dark spot on an incoherent background and is useful in some photometric situations. A simple formula is given for the approximate calculation of the excluded energy at large distances from the center of the diffraction pattern.
authors.forename: A T
authors.initials: AT
authors.lastname: Young