The effect of thickness gradients is studied using unfocused and focused beams in spectroscopic ellipsometry. A measurement with an ellipsometer in the polarizer-compensator sample analyzer (PCSA) configuration is extended to a triplet of raw data (psi, Delta, P) where P is the degree of polarization of the reflected beam. It is shown that an averaging scheme allows one to measure using a large beam diameter and that a correction using the measured degree of polarization works well for improving microspot measurements.