We investigate theoretically polarization effects occurring in infrared spectra of finite-size conducting samples. In ellipsometric data taken at grazing incidence, a strong influence of sample edges is observed even for sample dimensions of several hundreds of a wavelength. As usual, the ellipsometric technique is found to be very efficient in supplying both magnitudes and phases of the polarized light waves. We present a comparison of the calculations with experimental far-infrared data of copper. (C) 2004 Elsevier B.V. All rights reserved.