We solve the 3-D Bragg diffraction problem for a plane light wave, incident on a rectangular acoustic column, in the near zone of acousto-optic (AO) diffraction for the case of weak interaction. We show that the orientation of the boundaries of the acoustic column with respect to the incident light wave vector influences the direction of the diffracted light. It appears that the wave vector of the diffracted light is not necessarily coplanar with the wave vector of the incident light and the central wave vector of the sound column. The angle of deviation of the wave vector for the diffracted light is calculated. Conditions for applying the standard solution of the 2-D AO problem are studied. The problem is solved using the 4-D spectral representation of wave fields method.