Abstrakt
Light from a distant quasar passing in the vicinity of a foreground galaxy may be deflected by its gravitational field. According to the Fermat principle multiple macro-images of the quasar can then be observed.
In addition, the light can be affected by the gravitational field of individual stars moving in the lensing galaxy, creating multiple micro-images. We cannot resolve them because of their small angular separation, but we can observe an associated increase of the flux.
We will discuss how to model this phenomenon and related observable effects.