Abstract
We introduce the idea of shape parameters to describe the shape of the pencil of rays connecting an observer with a source lying on his past light cone. On the basis of these shape parameters, we discuss a setting of image distortion in a generic (exact) spacetime, in the form of three distortion parameters. The fundamental tool in our discussion is the use of geodesic deviation fields along a null geodesic to study how source shapes are propagated and distorted on the path to an observer. We illustrate this nonperturbative treatment of image distortion in the case of lensing by a Schwarzschild black hole. We conclude by showing that there is a nonperturbative generalization of the use of Fermat’s principle in lensing in the thin-lens approximation.
- Received 4 August 2000
DOI:https://doi.org/10.1103/PhysRevD.63.023006
©2000 American Physical Society