Spectro-polarimetry plays an important role in the study of solar magnetism and strongly influences the design of the new generation of solar telescopes. Calibration of the polarization properties of the telescope is a critical requirement needed to use these observations to infer solar magnetic fields. However, the large apertures of these new telescopes make direct calibration with polarization calibration optics placed before all the telescope optical elements impractical. It is therefore desirable to be able to infer the polarization properties of the telescope optical elements utilizing solar observations themselves. Taking advantage of the fact that the un-polarized, linearly, and circularly polarized spectra originating from the Sun are uncorrelated, we have developed techniques to utilize observations of solar spectra with redundant combination of the polarization states measured at several different telescope configurations to infer the polarization properties of the telescope as a whole and of its optical elements. We show results of these techniques applied to spectro-plarimetric data obtained at the Dunn Solar Telescope.