  A method to calculate the statistical properties of microlensing light curves
is developed. The approach follows works by Deguchi & Watson, Seitz & Schneider
and Neindorf, attempting to clarify the ideas involved and techniques used in
the calculations. The method is then modified to include scattering by multiple
lensing planes along the line of sight and transition to a continuous limit of
this treatment for average quantities is performed leading to a Fokker-Planck
type equation. The equation is solved for a particular model of the random star
field and microlensing effect on the flux temporal variability is extracted.
Applications in astrophysically relevant situations are discussed.
