  The polarization effect of the 31 reflections within the mirror train of an
auxiliary telescope of the Very Large Telescope Interferometer is calculated as
a function of pointing direction and rotator angle. With a rough estimate of
the mean complex index of refraction of the reflecting surfaces, their Jones
matrices are concatenated while tracing a ray from M1 up to the feeding mirror
in front of an instrument. The net effect is summarized in terms of the axis
ratio of the polarization ellipse of star light that was circularly polarized
above the primary mirror.
