The European Solar Telescope (EST) will provide spectro-polarimetric measurements of the solar atmosphere with unprecedented sensitivity and accuracy. To this purpose, its optical scheme, as well as its MCAO system, are designed to minimize the instrumental polarization. In the framework of the EST design, we have started a series of laboratory tests to characterize the effects of using deformable mirrors on polarization measurements. In this contribution, we will show the results of these tests. These results are not only relevant to solar physics, but also to a number of other astrophysical research fields where high precision polarimetry is becoming a fundamental tool, such as for example exoplanets detection, and star formation characterization.