Ehlers, Jürgen Geometric Analysis and Gravitation, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
332998.pdf (Verlagsversion), 2MB
Seitz, S., Schneider, P., & Ehlers, J. (1994). Light-propagation in arbitrary spacetimes and the gravitational lens approximation. Classical and Quantum Gravity, 11(9), 2345-2373. doi:10.1088/0264-9381/11/9/016.