  Treatments of Fraunhofer diffraction normally approximate the inclination
factor in the diffraction integral by 1, but this is not necessary. In this
paper, the Rayleigh-Sommerfeld diffraction integral is used and a complete
description of Fraunhofer diffraction is given, with the minimum possible
number of approximations made. A focused wave is examined before, at, and after
its focal point to elucidate the exact role of the Fourier transform in
describing Fraunhofer diffraction and to derive the Guoy phase shift.
