Image distortion from optical scalars in nonperturbative gravitational lensing - art. no. 023007

In a previous article concerning image distortion in nonperturbative gravit ational lensing theory we described how to introduce shape and distortion p arameters for small sources. We also showed how they could be expressed in terms of the scalar products of the geodesic deviation vectors of the sourc e's pencil of rays in the past light cone of an observer. In the present wo rk we give an alternative approach to the description of the shape and dist ortion parameters and their evolution along the null geodesic from the sour ce to the observer, but now in terms of the optical scalars (the convergenc e and shear of null vector field of the observer's light cone) and the asso ciated optical equations, which relate the optical scalars to the curvature of the spacetime.