  One of the main design goals of the MAGIC telescopes is the very fast
repositioning in case of Gamma Ray Burst (GRB) alarms, implying a low weight of
the telescope dish. This is accomplished by using a space frame made of carbon
fiber epoxy tubes, resulting in a strong but not very rigid support structure.
Therefore it is necessary to readjust the individual mirror tiles to correct
for deformations of the dish under varying gravitational load while tracking an
object. We present the concept of the Active Mirror Control (AMC) as
implemented in the MAGIC telescopes and the actual performance reached.
Additionally we show that also telescopes using a stiff structure can benefit
from using an AMC.
