  Diffraction limited 30m class telescopes will play an important role in
gravitational lensing studies, coming online in approximately 2015. As imaging
telescopes they will complement the ~6m JWST, probing to smaller angular scales
in greatly magnified objects near critical lines and for measuring shear of
objects below the JWST angular scale, such as luminous super-star clusters at
high redshift. The high source density will allow more detailed mass mapping in
the weak lensing regime and will be useful in breaking the cosmology-lens
potential degeneracy in strong lensing. As multi-object spectrographs 30m
telescopes should provide spectra over the entire optical and near infrared
spectrum region. The statistical distribution of redshifts needed to invert
projected shear measurements and calibration of photometric redshifts for
``tomography'' will be available to flux levels around 5-10 nano-Jansky (approx
29.5 m_AB). However, a one nJy object is expected to require ~500 hours to
acquire a redshift, which is most of the dark time in an observing season.
Accordingly ``gravitational telescopes'' will be an important tool for probing
the very faint high redshift universe, magnifying a few square arc-seconds at a
time by factors of 10-1000.
