We employ an optimal solution to both the "shape from motion problem" and the related problem of the estimation of self-movement on a purely optical basis to deduce practical rules of thumb for the limits of the optic flow information content in the presence of perturbation of the motion parallax field. The results are illustrated and verified by means of a computer simulation. The results allow estimates of the accuracy of depth and egomotion estimates as a function of the accuracy of data sampling and the width of field of view, as well as estimates of the interaction between rotational and translational components of the movement.