The change in the apparent luminosity and shape of distant light sources due to inhomogeneities in the Universe that cause gravitational deflections of the light rays is discussed. The case explored in most detail is a static universe with randomly distributed mass points and with pointlike light sources. Ray-tracing technique by means of a computer is used. It is shown that the results found in the case of static and flat universes in most cases can be applied to expanding and curved universes with fairly good approximation. The validity of the point-source and point-deflector approximation is briefly examined, and the changes one has to expect if the approximation is not valid are indicated.