Gravitational lenses in arbitrary space-times

The precision reached by current and forthcoming strong-lensing observations requires to accurately model various perturbations the main deflector. Hitherto, theoretical models have been developed account for either cosmological line-of-sight perturbations, or isolated secondary lenses via multi-plane lensing framework. This article proposes a general formalism describe multiple within an arbitrary space-time background. lens equation, expressions of amplification time delays, are rigorously derived in that Our results may be applied wide range set-ups, from strong anisotropic cosmologies, beyond tidal regime.