  We demonstrate the use of an ordinary white-light microscope for the study of
the q-dependent dynamics of colloidal dispersions. Time series of digital video
images are acquired in bright field with a fast camera and image differences
are Fourier-analyzed as a function of the time delay between them. This allows
for the characterization of the particle dynamics independent on whether they
can be resolved individually or not. The characteristic times are measured in a
wide range of wavevectors and the results are found to be in good agreement
with the theoretically expected values for Brownian motion in a viscous medium.
