Single-ring polanret phase-contrast system.

An extremely simple, modified polanret phase-contrast system has been developed. It uses only a single polarizing ring, instead of three zonal polarizers as required in Osterberg's original polanret system (manufactured by the American Optical Corporation). The modified system is much more easily manufactured and its economy of light is twice as good. However, it does require an easily accessible microscope objective exit pupil, where the polarizing ring must be located.