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

当前和即将进行的强透镜观测所达到的精度要求准确模拟对主偏转器的各种扰动。迄今为止，已经开发了理论模型来解释宇宙学视线扰动或通过多平面透镜框架隔离的次级透镜。本文提出了一种通用形式来描述任意时空背景中的多个镜头。透镜方程，以及放大和时间延迟的表达式，都是在该框架中严格推导出来的。我们的结果可以应用于广泛的设置，从各向异性宇宙学中的强透镜，到潮汐状态之外的视线扰动。