  The response of the ``perfect lens'', consisting of a slab of lossless
material of thickness $d$ with $\epsilon=\mu=-1$ at one frequency $\omega_0$ is
investigated. It is shown that as time progresses the lens becomes increasingly
opaque to any physical TM line dipole source located a distance $d_0<d/2$ from
the lens and which has been turned on at time $t=0$. Here a physical source is
defined as one which supplies a bounded amount of energy per unit time. In fact
the lens cloaks the source so that it is not visible from behind the lens
either. For sources which are turned on exponentially slowly there is an exact
correspondence between the response of the perfect lens in the long time
constant limit and the response of lossy lenses in the low loss limit. Contrary
to the usual picture where the field intensity has a minimum at the front
interface we find that the field diverges to infinity there in the long time
constant limit.
