Some embodiments include a system having a polarizer and an analyzer to define a light transmission axis. Both the polarizer and the analyzer have a polarization transmission direction, which is substantially perpendicular to the light transmission axis. A first waveplate and a second waveplate are is interposed between the polarizer and the analyzer, such that both waveplates are located along the light transmission axis. Both waveplates have a slow axis, which is substantially perpendicular to the light transmission axis. The first waveplate is rotated about the light transmission axis, such that the slow axis of the first waveplate is at an angle with a polarization transmission direction of the polarizer. The analyzer is rotated about the light transmission axis until the light transmitted through the system is minimized. The first waveplate and the analyzer are recursively rotated until an extinction angle is determined.