Small-angle X-ray diffraction from synthetic opal films has been investigated as a function of the orientation of the sample. All the observed (hkl) diffraction reflections have been interpreted. The reconstruction of the reciprocal lattice of the studied opal films has been carried out. The diffraction patterns and scattering intensity profiles along chains of reciprocal lattice points have been calculated. It has been shown that, in the reconstructed reciprocal lattice of the opal films, the appearance of chains of partially overlapping nodes that are oriented along the direction Γ → L is caused by two factors: the small thickness of the film and the existence of stacking faults in it.