  By comparing the results of numerical microlensing simulations to the
observed long-term variability of quasars, strong upper limits on the
cosmological density of compact objects in the mass range 0.01 to 0.0001 solar
masses may be imposed. Using recently developed methods to better approximate
the amplification of large sources, we investigate in what way the constraints
are affected by assumptions concerning the size of the optical
continuum-emitting region of quasars in the currently favored (Omega_M=0.3,
Omega_Lambda=0.7) cosmology.
