A manual null ellipsometer is constructed and used to determine the optical constants of zinc and cadmium of different surface roughness at the wavelength 632.8 nm, angle of incidence 45° and room temperature. The studied samples are polycrystalline sheets of thickness ~ 0.05 mm and surface area 30 mm x 30 mm. The samples were mechanically polished using diamond paste of different grain sizes. The final stage of polishing for the samples was with pastes of grain size 0.5 μm, 2.5 μm, 5 μm, 10 μm and 14 μm. The ellipsometric parameters  and  were obtained and were used to calculate the optical constants  (refractive index) and  (extinction coefficient).It was found that as the roughness is increased, the refractive index  increases while the extinction coefficient  decreases. The used optical arrangement for ellipsometric measurements is presented and the procedure for extracting the results is explained. The uncertainty in the results is calculated and included in the results.