  We present an in-depth weak lensing analysis of the cluster MS1008 based on
deep multicolor imaging obtained during the Science Verification of FORS1 at
the VLT. The image quality (half arcsec seeing) and depth of the VLT images
allow the shear signal to be mapped with high signal-to-noise and to be traced
out to 1.2 h_50^-1 Mpc, near the edge of the 6'.8x6'.8 field of view. Using
BVRI color information, as well as 81 redshifts in the field from the CNOC
survey, background galaxies can be effectively separated from cluster and
foreground objects. PSF distorsions are found to be moderate across the FORS
images and thus easily removed. Due to the small statistical errors in the mass
reconstruction, this dataset provides a testing ground where several systematic
effects (e.g. mass-sheet degeneracy, redshift distribution of the background
sources, cluster galaxy contamination) can be quantified. Several methods are
used to remove the mass-sheet degeneracy which is found to dominate the
systematic error budget. We measure a lower limit to the mass of 2.6 10^14
h_50^-1 M_sun within 1 h_50^-1 Mpc and a ``total'' mass of 5.3 10^14 h_50^-1
M_sun by fitting a softened isothermal sphere. The availability of the CNOC
redshift data and X-ray observations on this cluster allow a comparison of
different determinations of the mass radial profile. We find the lensing and
X-ray measurements in excellent agreement, while the mass derived from the
virial analysis is marginally (1-2 sigma) in agreement at radii where both
methods are reliable.
