A procedure has been developed for the accurate measurement of film and substrate optical parameters from the multiple sample single-wavelength ellipsometric data. The dimensional reduction of the unknowns from newly formulated ellipsometric functions, the root selection and the thickness-dependent integer deduction enhance the rapidity of finding solutions and the convergence from a wide range of initial guesses while avoiding undesirable solutions. An error analysis carried out shows that the procedure is very resistant to the propagation of angular errors and allows the estimation of optimum film thickness ranges under which the parameters can be accurately found. The standard SiO2/Si structure is particularly studied using the procedure that is further illustrated with the experimental data on Ni/BK7-glass structures. The SiO2 film refractive index and thickness are thus shown to be accurately determined when sought along with the substrate optical constants. Moreover, the film and substrate real indexes are not altered in the presence of an interface layer between the film and the substrate while its existence is indicated by a systematic lowering of the Si substrate extinction coefficient. The procedure can be efficiently used in the continuous real-time optical characterization of films growing on substrates.