Gravitational Lensing and Microlensing in Clusters: Clusters as Dark
  Matter Telescopes
  Gravitational lensing is brightening of background objects due to deflection
of light by foreground sources. Rich clusters of galaxies are very effective
lenses because they are centrally concentrated. Such natural Gravitational
Telescopes provide us with strongly magnified galaxies at high redshifts
otherwise too faint to be detected or analyzed. With a lensing boost, we can
study galaxies shining at the end of the `Dark Ages'. We propose to exploit the
opportunity provided by the large field of view and depth, to search for
sources magnified by foreground clusters in the vicinity of the cluster
critical curves, where enhancements can be of several tens in brightness.
Another aspect is microlensing (ML), where we would like to continue our survey
of a number of Galactic globular clusters over time-scales of weeks to years to
search for ML events from planets to hypothesized central intermediate-mass
black holes (IMBH).
