Peculiarities of collinear acousto-optic interaction of a strongly divergent optical beam are examined theoretically by examples of two crystals widely used in acousto-optics: calcium molybdate ( $\mathrm{Ca}\mathrm{Mo}{\mathrm{O}}_4$ ) and paratellurite ( $\mathrm{Te}{\mathrm{O}}_2$ ). These materials demonstrate essentially different diffraction characteristics because of peculiar features of optical and acousto-optic anisotropy in these crystals. The dependence of the integral diffraction efficiency and the transmission band of collinear acousto-optic filters on the optical beam divergence and acoustic power is studied. It is shown that with increasing light divergence these characteristics of the filter are worsened according to the same law, and the product of the relative bandwidth and the diffraction efficiency remains constant and independent of the optical wavelength and the acousto-optic interaction length.