  We investigate the wave optics in the Schwarzschild spacetime. Applying the
standard formalism of wave scattering problems, the Green function represented
by the sum over the partial waves is evaluated using the Poisson sum formula.
The effect of orbiting scattering due to the unstable circular orbit for null
rays is taken into account as the contribution of the Regge poles of the
scattering matrix and the asymptotic form of the scattering wave is obtained in
the eikonal limit. Using this wave function, images of the black hole
illuminated by a point source are reconstructed. We also discuss the wave
effect in the frequency domain caused by the interference between the direct
rays and the winding rays.
