We take advantage of a spectroscopic ellipsometer that can operate in both rotating-analyzer (RAE) and rotating-compensator (RCE) modes to compare directly the capabilities of the two configurations. The extra information available from the additional Fourier component of the transmitted intensity for the RCE provides considerable advantages both with respect to identifying artifacts and obtaining more accurate data. For example, our comparison revealed a previously unsuspected polarization-leakage artifact that affects RAE data to as much as several percent. Comparative measurements on Ge and ZnO show the RCE has greatly reduced sensitivity to artifacts in general, and particularly those resulting from wavelength-averaging interference effects in thin films. (C) 2003 Elsevier B.V All rights reserved.