Issues in a broadband 4-channel reduced Stokes polarimeter

In this paper we outline and address some of the challenges encountered in calibrating a visible 4-channel imaging reduced Stokes polarimeter. Specifically we expose the errors associated with the retardance of the optical elements in the system and show how the presence of circular polarization can affect the measurement of the linear states of polarization. These errors are analyzed in some detail and several possible solutions are proposed.