A novel approach to the quantitative characterization of the regularity of the opal photonic crystal lattice based on a Fourier transform analysis of the azimuth rotational symmetry of the optical transmission is proposed. The magnitudes of three harmonics in the Fourier transform related to the two-, six- and twelvefold rotational symmetry of the transmission pattern have been suggested for quantification of the lattice ordering. The specific composition of these harmonics has been observed for the transmission attenuation at different lattice planes. The diffraction at (220) and (200) families of crystal planes has been identified as the most sensitive to the crystallinity of the opal lattice. The transmission pattern obtained in the s-polarized light is recommended for comparison.