  Gravitational lensing studies of the Bullet Cluster suggested convincingly in
favor of the existence of dark matter. However, it was performed without the
knowledge of the original orientation of each galaxy before gravitational
lensing. A potential improvement to this issue lies in the measurement of the
original orientation from the polarization direction of radio waves emitted
from each galaxy. In this context, Francfort et al. derived a formula that can
utilize the information about the original orientation of each galaxy to obtain
what is called {\it shear}. However, we demonstrate that shear in their formula
should be replaced by {\it reduced shear} when the change in sizes of images of
galaxies is taken into account. As the previous gravitational lensing analysis
of the Bullet Cluster used reduced shear, we suggest applying our improved
formula directly for the reanalysis once we obtain the polarization direction
of radio waves. In particular, we show that our new formula can yield a more
accurate analysis than the previous one, if the polarization direction can be
measured more precisely than $10^\circ$. Moreover, the approach discussed in
this work is generically applicable to the gravitational lensing analysis of
clusters, not only limited to the Bullet Cluster.
