  We study the gravitational lensing in the weak field approximation assuming
the presence of a plasma and of a magnetic field around a compact gravitational
source. The external magnetic field causes the split of the image, as the
counterpart of the Zeeman effect. The magnetic field affects the magnification
of images, creating additional components. We also study the time delay of an
electromagnetic signal due to the geometry and the gravitational field around
the source. We show that the time delay strongly depends on the plasma
parameters. Lastly, we consider the effects of the presence of an inhomogeneous
plasma on the gravitational lensing.
