1994A&A...288...19S

Using the method of correlated deflection probabilities of microlensed light rays, we show how to determine the magnification auto-correlation function and the magnification fluctuations in various microlensing situations. We compare our results with those obtained with other methods, and investigate the practical limitations inherent in the ray-shooting method: finite resolution, and the problem of fair sampling of the source plane. We apply our method to the observed light curve of the microlensed image A of Q2237+0305 and determine correlation times and magnification fluctuations. We conclude that it is possible to explain this light curve with low-mass lenses.