  We give an estimate of the relative error in the angular measurement of
observations for high redshift objects induced by gravitational scatterings
(lensing). Gunn (1967) concluded that the gravitational scatterings by galaxies
induce the relative error of a few percent in the observations for objects at
$z=1$. This estimate has been considered as a fundamental limitation of
accuracy of the angular measurements in the observational cosmology. In
multiple graviational scatterings, bending angle of single ray grows through
the random work process. Gunn (1967) assumed that the difference of nearby rays
also grows through the random walk process. However, distance between nearby
photons grows exponentially because the two rays suffer coherent scatterings by
the same scattering object. This exponential growth continues as long as the
scattering is coherent. In the case of scattering by individual galaxies, the
exponential growth continues until the angular distance reaches an arcminute or
so. The relative error of the angular measurements under an arcminute due to
the exponential growth is $\sim 30\%$ at $z=1$ and exceeds $100\%$ at $z=3$, in
the case that the density parameter of galaxies is 0.2. The effects of clusters
of galaxies or superclusters are more difficult to estimate accurately, but
might be significant. In the case of supercluster the angular measurements up
to a few degrees could be affected.
