  Aims: We measure the redshift of the lensing galaxy in eight gravitationally
lensed quasars in view of determining the Hubble parameter H_0 from the time
delay method.
  Methods: Deep VLT/FORS1 spectra of lensed quasars are spatially deconvolved
in order to separate the spectrum of the lensing galaxies from the glare of the
much brighter quasar images. A new observing strategy is devised. It involves
observations in Multi-Object-Spectroscopy (MOS) which allows the simultaneous
observation of the target and of several PSF and flux calibration stars. The
advantage of this method over traditional long-slit observations is a much more
reliable extraction and flux calibration of the spectra.
  Results: For the first time we measure the redshift of the lensing galaxy in
three multiply-imaged quasars: SDSS J1138+0314 (z=0.445), SDSS J1226-0006
(z=0.517), SDSS J1335+0118 (z=0.440), and we give a tentative estimate of the
redshift of the lensing galaxy in Q 1355-2257 (z=0.701). We confirm four
previously measured redshifts: HE 0047-1756 (z=0.407), HE 0230-2130 (z=0.523),
HE 0435-1223 (z=0.454) and WFI J2033-4723 (z=0.661). In addition, we determine
the redshift of the second lensing galaxy in HE 0230-2130 (z=0.526). The
spectra of all lens galaxies are typical for early-type galaxies, except for
the second lensing galaxy in HE 0230-2130 which displays prominent [OII]
emission.

Astrophysics