  The amplification caused by gravitational light bending by compact objects in
a foreground galaxy can affect the apparent number density of background QSOs,
as well as their distribution in the fields of galactic halos. In this work we
investigate the number enhancement of QSOs in the fields of galactic halos
caused by point mass lensing effect and singular isothermal lensing effect, and
apply the microlensing effect due to dark compact objects in the halo to NGC
3628. NGC 3628 is a well-studied nearby edge-on Sbc peculiar galaxy, where QSOs
are shown to be concentrated around the galaxy with a density much higher than
background. We show that if present understanding of the luminosity function of
QSOs is right, such concentration could not be caused by gravitational lensing.
