A real-time measurement of the polarization of faint light is brought forward, and it has many promising applications. The measure can be actualized by a partially polarizing beam splitter and two polarizing beam splitters. Two phasic-compensators are appended to optimize the system. The optimization theory is educed, and the optimized apparatus matrix is given. An optimal polarimeter is given. Its Muller matrix is approached to ideal, and the error is less 0.25%. The setup is able to reconstruct the stokes vector of any input polarization to a fidelity of at least 97%.